21 Best Products to Sell on a Free Online Store With Healthy Margins

Some links on The Justifiable are affiliate links, meaning we may earn a small commission at no extra cost to you. Read full disclaimer.

The best products to sell on a free online store are not necessarily the trendiest items. They are products you can test cheaply, price with enough room for fees and fulfillment, and explain clearly to a specific buyer.

A free storefront reduces one fixed cost, but it does not protect you from weak margins, expensive shipping, or unsold inventory.

This guide shows you 21 practical product ideas, why each can work, and how to validate them before committing serious cash. You will also learn how to price, troubleshoot, and scale the products that prove themselves.

What Makes a Product Worth Selling on a Free Online Store

A zero-cost storefront can lower the barrier to entry, but product economics still decide whether the business works. Favor simple catalogs, low inventory risk, manageable fulfillment, and products with a clear reason for buyers to choose your version.

Calculate Contribution Margin Before You Choose a Product

Gross margin is useful, but contribution margin gives you a clearer picture of what each order actually adds to the business. Start with the selling price, then subtract the product cost, packaging, payment fees, shipping subsidies, fulfillment expenses, and any other variable cost tied directly to that order. What remains must help cover advertising, software you add later, returns, and profit.

For example, imagine you sell an item for $30. The product costs $8, packaging costs $2, payment and transaction costs total $2, and you spend $3 subsidizing shipping. Your contribution before advertising is $15.

A cheap product with a low selling price can be harder to scale than a more expensive item because fixed per-order costs consume a larger share of revenue. Healthy margins come from the entire order equation, not from sourcing cheaply alone.

Small, light, durable products also give you more flexibility than bulky or fragile goods. Add niche positioning, personalization, useful bundles, original design, convenience, or specialized knowledge, and you have more ways to compete without automatically becoming the cheapest seller.

A product is not “high margin” because the supplier price looks low. It is high margin only when enough money remains after the real costs of making the sale.

Digital Products With Very Low Fulfillment Costs

Digital goods are attractive for a free store because you can create an asset once and sell it repeatedly without holding physical inventory. The challenge is not delivery cost; it is creating something specific enough that buyers see an immediate reason to pay.

1. Printable Planners and Trackers

Printable planners work best when they solve a narrow planning problem rather than trying to become another generic daily planner. Think meal-prep sheets for busy families, wedding budget trackers, debt payoff calendars, homeschool lesson planners, strength-training logs, or maintenance checklists for short-term rental hosts.

The stronger opportunity comes from bundling. A single printable page may feel disposable, while a coordinated 20-page system can feel like a complete solution.

Start with one use case and build around the steps that buyer already takes. If you are targeting new freelancers, for example, combine an income tracker, invoice log, client follow-up sheet, quarterly planning page, and tax-document checklist.

The main mistake is overdesigning. Buyers usually value clarity, printability, and ease of use more than decorative complexity. Test your files on standard paper sizes, include simple instructions, and show preview images that make the outcome obvious. Once one pack generates steady interest, you can expand with companion pages without adding inventory or changing your fulfillment process.

2. Editable Template Packs

Editable templates can serve businesses, creators, teachers, clubs, event organizers, and job seekers. Strong examples include social post layouts, media kits, service menus, client onboarding documents, price lists, presentation layouts, lead magnets, and event signage.

The key to healthy margins is selling a system rather than isolated designs. A service business may value a coordinated pack containing a price list, welcome guide, testimonial graphic, and promotional post. That increases perceived value without increasing delivery costs in the same way a physical bundle would.

Choose a buyer with recurring design needs, then make customization simple with clear placeholders, consistent sizing, sensible hierarchy, and brief instructions.

Also be careful with licensing. Use graphics, fonts, and design elements you have the right to redistribute in the way your product requires. Your listing should explain what the buyer may edit, where they can use the finished design, and whether commercial use is included. Clear boundaries reduce refund requests and support questions while making the product easier to buy confidently.

3. Niche Guides, Checklists, and Mini Handbooks

A short digital guide can sell when it saves the reader research time or helps them complete a task with fewer mistakes. The profitable angle is specificity. “How to Get Organized” is vague; “Weekend Move-Out Checklist for Renters” has a defined user, situation, and desired result.

A concise handbook paired with checklists, worksheets, or scripts can be more useful than a long ebook. A guide for first-time craft fair vendors, for example, might include a packing checklist, booth layout planner, pricing worksheet, and day-of setup sequence. The buyer is paying for a smoother process, not for page count.

Choose subjects where you can provide real, non-deceptive value. Avoid regulated professional advice unless you are qualified and can meet the relevant requirements. You should also update products when laws, platform rules, or procedures change.

For validation, describe the outcome before creating the full guide and test whether people click, join a waitlist, or preorder. If it sells, expand into companion resources rather than jumping to an unrelated niche.

4. Niche Spreadsheets and Calculators

Spreadsheets can command better prices than simple printables when they perform useful calculations or organize messy decisions. Examples include freelance project profitability sheets, inventory reorder calculators, content planning workbooks, renovation budgets, event cost planners, commission trackers, and resale profit calculators.

The best spreadsheet products reduce mental work. Instead of asking the buyer to build formulas, categories, and dashboards from scratch, you give them a tested structure. Keep the first screen simple, label inputs clearly, protect cells that should not be edited when possible, and include a small sample so users understand how the tool behaves.

A basic workbook can solve one task, while a larger bundle adds forecasting or scenario tabs without creating physical inventory.

Testing is essential because spreadsheet errors damage trust quickly. Run realistic edge cases, try blank inputs, test large and small numbers, and ask someone unfamiliar with the file to use it without your help. A technically impressive workbook is still a weak product if the buyer cannot understand what to enter.

Print-on-Demand and Personalized Products

Print-on-demand and personalization let you sell physical goods without buying large quantities upfront. Margins depend heavily on design quality, supplier costs, shipping, and pricing, so the safest approach is to target a defined niche rather than compete with generic merchandise.

5. Niche Print-on-Demand T-Shirts

T-shirts remain a practical starter product because buyers already understand the format and niche designs can carry emotional value. The opportunity is not “funny shirts” in general. It is a shirt that feels made for a particular identity, hobby, profession, local community, event, or shared joke.

Keep your first collection focused. Three strong designs for one audience are easier to market than thirty unrelated graphics. Use mockups carefully, but order a sample before promoting heavily so you can check print placement, fabric feel, sizing, and packaging.

Margins can become tight when production and shipping costs are high, so do not price by copying the cheapest marketplace seller. Work backward from the contribution you need after fulfillment. If the price feels too high for a plain shirt, improve the concept, presentation, or audience specificity rather than immediately cutting margin.

Avoid trademarked slogans, logos, characters, and celebrity references you do not have permission to use. A strong niche idea still needs to be legally sellable.

6. Print-on-Demand Tote Bags

Tote bags offer a useful middle ground between apparel and home accessories. They avoid clothing-size complexity and suit identity, gifting, events, hobbies, or everyday use.

The strongest concepts combine design with context. A generic floral tote is easy to compare on price. A tote designed for library volunteers, knitting groups, teachers, gardeners, book clubs, or conference attendees has a clearer reason to exist. You can also personalize names, dates, locations, or short phrases when your fulfillment process supports it.

To protect margins, pay attention to print area, bag weight, base cost, and shipping method. A low-cost blank does not help if the finished product looks thin or arrives creased and disappointing. Order samples and photograph details that customers care about, such as handle length, interior capacity, and print texture.

Totes also bundle well with smaller products. A book-themed store could pair a tote with bookmarks and annotation tabs. The bundle raises average order value while keeping the customer inside one coherent niche rather than pushing unrelated add-ons.

7. Sticker and Decal Packs

Sticker packs can work well because they are light, inexpensive to ship, and easy to theme around a specific community or use case. Planner decals, water-bottle graphics, hobby labels, and packaging stickers all move beyond one-off novelty designs.

Single stickers often create a margin problem because the order value is low compared with payment and fulfillment costs. Packs are usually more practical. Group five to twelve coordinated designs around one theme, then price the set as a complete collection. You can also offer a larger bundle for customers who want duplicates or multiple sizes.

State clearly whether stickers are removable, water resistant, outdoor-suitable, or made for a particular surface. If you fulfill in-house, test cutting, adhesion, and packaging before scaling.

This category also gives you a fast product-development loop. New designs are relatively easy to prototype, which means you can release small themed drops, observe what sells, and turn winning concepts into larger collections or related merchandise later.

8. Personalized Wall Art and Small Prints

Personalized wall art can support stronger margins because the buyer is purchasing meaning as much as paper and ink. Family name prints, pet portraits, location maps, wedding dates, and hobby illustrations can target a specific moment or recipient.

The operational challenge is personalization accuracy. Build a clear order form, show exactly what information the customer must provide, and create a repeatable proofing process if you offer previews. Every manual message adds labor, so simplify the workflow before increasing order volume.

Small standard print sizes are easier to ship and frame than oversized artwork. You can offer digital-only delivery, physical prints, or both, but keep the options easy to understand. If you outsource printing, order samples so you know how colors, paper, trimming, and packaging look in real life.

A common mistake is accepting unlimited revisions. That can destroy an otherwise healthy margin. Define what personalization includes, how many changes are allowed, and what counts as a new request. Clear boundaries make the buying experience better for both sides.

Lightweight Accessories That Ship Efficiently

Small accessories can produce attractive order economics because they are easy to store, photograph, and bundle. They still need differentiation, so focus on design, niche relevance, material quality, or a useful set rather than selling interchangeable commodity items.

9. Simple Fashion Jewelry

Small jewelry pieces such as minimalist earrings, charm bracelets, simple necklaces, and niche-themed pins are easy to store and inexpensive to ship compared with larger products. They can also carry strong perceived value when the design, packaging, and audience are aligned.

You can make pieces, assemble components, or source finished items, but always disclose materials accurately. Buyers may care about plating, base metals, nickel content, care instructions, and whether an item is suitable for sensitive skin. Do not make claims you cannot verify.

Healthy margins often come from presentation and sets. A pair of earrings placed in a thoughtful gift card and protective pouch feels different from a loose item in generic packaging. You can also sell two- or three-piece combinations around a theme.

The biggest risk is undifferentiated sourcing. If customers can find the exact item everywhere, price pressure increases quickly. Look for original assembly, custom packaging, a niche design language, personalization, or limited collections that give your store a recognizable point of view.

10. Hair Accessory Sets

Hair accessories are compact, familiar, and easy to bundle. Scrunchies, claw clips, headbands, barrettes, and bow sets can be organized by style, hair type, color palette, occasion, or age group without requiring a large investment in each individual SKU.

Bundles are particularly useful here because a single low-priced accessory may not leave enough contribution after payment fees and packaging. A three-piece neutral set, a travel hair kit, or a coordinated event pack creates a more meaningful order value while giving the buyer an easy choice.

Quality control should focus on the points that cause disappointment: weak springs, rough edges, poor stitching, color mismatch, or sizes that do not match the listing photos. If you source products, order a small batch first and test them through normal use rather than judging from supplier images.

Keep a core collection year-round, then add small seasonal drops for weddings, school periods, holidays, or travel. This adds novelty without bloating the catalog.

11. Phone Straps and Charms

Phone straps, wristlets, bead charms, and decorative lanyards are small enough for low-cost shipping and flexible enough for personalization. Initials, color combinations, hobby references, and custom bead selections can strengthen the offer.

The first operational question is compatibility. Some straps attach through a phone case opening, while others require a specific tab or connector. Explain what the customer needs and show close-up photos of the attachment method. Preventing compatibility confusion is cheaper than processing returns.

If you hand-assemble the product, time your production process. A design that takes twenty minutes longer than expected can quietly erase your margin even when materials are cheap. Create a small menu of standardized options instead of offering unlimited custom combinations.

Durability is another important issue because the product may carry an expensive phone. Avoid promising protective performance unless you have evidence to support it. Present the item as an accessory, inspect connections carefully, and include reasonable care guidance. A visually attractive product still needs consistent assembly to earn repeat purchases and referrals.

12. Bookmarks and Reading Annotation Kits

Book-related accessories are a strong niche option because they can be lightweight, giftable, and easy to organize into themed sets. Products can include magnetic bookmarks, page tabs, annotation flags, book sleeves, or coordinated reading kits.

The margin opportunity improves when you sell a useful experience rather than one bookmark. For example, an annotation kit could include color-coded tabs, a legend card, a pen loop, and two bookmarks. A book club pack could contain matching bookmarks and discussion prompt cards for several members.

Design matters, but functionality matters just as much. Magnetic bookmarks should close securely without damaging pages, tabs should be easy to remove if advertised that way, and printed elements should remain legible at small sizes. Test the kit with actual books instead of relying on mockups.

Romance readers, students, teachers, and book clubs can want very different aesthetics and tools. Choose one group first, then expand after you know which accessories they actually use.

Home, Desk, and Hobby Products With Bundle Potential

Practical products can sell without relying on fashion trends when they remove friction from an everyday task.

For a small free-store catalog, the best versions are compact, easy to demonstrate, and naturally suited to multipacks or kits.

13. Desk Cable-Management Kits

Cable management is a simple problem with visible before-and-after value. A compact kit might combine adhesive cable clips, reusable ties, labels, and a small cable sleeve for a home office, gaming desk, or study space.

Grouping complementary pieces can raise order value and give the buyer a complete solution without adding much shipping weight. Create different configurations only when the use case truly changes, such as a basic laptop desk kit versus a larger multi-device setup.

Your product page should show the kit installed in realistic situations. Include dimensions, adhesive surface guidance, and examples of cable thickness if relevant. Small accessories generate returns when buyers assume they are larger, stronger, or compatible with every surface.

Be careful with low-quality adhesives and brittle plastic. The product looks simple, but failure is obvious when clips fall off a desk after a day. Test samples on common surfaces and avoid claims that exceed your test results. Reliability is what turns a commodity-looking item into a product buyers can recommend.

14. Small Organization and Labeling Kits

Organization products sell best when the customer can immediately picture a mess becoming easier to manage. Instead of opening a store filled with random storage products, choose one micro-problem: pantry labels, cable labels, travel pouch labels, craft drawer tags, classroom bin markers, or moving-box organization sets.

A labeling kit can combine printed labels, blank extras, and a simple category guide. The value comes from giving the buyer a ready-made system rather than loose supplies.

Keep the kit compact and avoid products that depend on precise fit unless you provide measurements. If labels are removable, waterproof, freezer-safe, or suitable for a certain surface, verify those qualities before advertising them.

You can test demand cheaply by producing a limited batch around one use case. Watch which label names customers request, which sizes they choose, and which add-ons appear repeatedly. Those signals can guide the second version of the kit more reliably than guessing at a huge catalog from day one.

15. Small DIY Craft Kits

DIY craft kits combine products, instructions, and an experience, which can justify a better selling price than the raw components alone. Examples include bracelet kits, beginner embroidery packs, paper-flower kits, or seasonal ornament kits.

Choose a project that a beginner can finish without specialized equipment. The more extra tools the customer must buy, the harder your offer becomes to explain. Include measured quantities, clear instructions, and a finished-project image that sets realistic expectations.

Your margin calculation must include assembly labor. Counting beads, cutting cord, printing instructions, and packing components can take longer than expected. Time yourself making ten kits, not one, and use the average labor in your pricing model.

Craft kits also create natural expansion paths. If one beginner project sells consistently, you can release a second design, refill materials, or a larger bundle. Avoid adding unrelated crafts too quickly. A recognizable niche—such as modern embroidery for beginners—is easier to market than a store that sells a different hobby every week.

Pet and Personal-Use Accessories

Pet owners and self-care shoppers often buy small accessories for utility, gifting, or personalization. The safest margin opportunities for a new seller usually come from non-ingestible, non-medicated products that are easy to describe and fulfill.

16. Personalized Pet Tags

Pet tags are compact, low-weight, and naturally personalized, which can reduce direct price comparison when your design feels distinctive. You can offer names, phone numbers, short phrases, colors, shapes, or illustrated motifs while keeping the underlying production process standardized.

The most important task is preventing personalization errors. Your order form should make character limits, capitalization, icon choices, and engraving layout clear. If customers must submit a phone number, show exactly where it will appear. A preview example can reduce misunderstandings even if you do not provide individual proofs.

Material and attachment details also matter. State dimensions, weight, finish, and what hardware is included. Avoid durability or safety claims you cannot substantiate, especially for products that may be worn every day.

To protect your time, limit the number of customization choices at launch. Five shapes and six finishes may sound exciting, but each option increases production complexity. Start with the combinations you can produce consistently, then use order data to decide which variants deserve expansion.

17. Pet Bandanas and Bow Ties

Pet bandanas and bow ties are attractive for a small store because they are visually marketable, giftable, and easy to release in seasonal collections. Sizing is the main source of friction. Use a clear measurement guide based on the way the product actually fits, and show where the owner should measure. Avoid relying only on breed examples because animals within the same breed can vary significantly.

If you sew items yourself, standardize patterns and production time. If you source them, check stitching, closures, washability, and fabric consistency across batches. A product that looks good in a photo can still create returns if it twists, frays, or fits unpredictably.

You can increase average order value with coordinated pairs or small occasion bundles, such as a bandana plus matching bow tie. Keep comfort and normal pet use in mind, and never position decorative accessories as safety equipment. Clear product boundaries protect trust while letting design and personalization carry the value.

18. Self-Care Accessory Sets

You can sell into the self-care category without manufacturing skincare or making health claims. Non-cosmetic accessory sets might include a sleep mask, soft headband, reusable cosmetic pads, hair wrap, toiletry pouch, or simple spa-style storage pieces.

The strongest offer is usually a themed set with a specific context. A “travel wind-down kit,” for example, is easier to understand than five unrelated accessories. A gift-ready presentation can raise perceived value further without adding a regulated formula to your catalog.

Material descriptions should be accurate. If you describe a fabric as silk, bamboo, organic, hypoallergenic, or another specific material or quality, make sure you can support that statement. It is better to use precise, modest language than to overpromise.

Watch packaging costs because giftable sets can become expensive if you add oversized boxes, filler, ribbons, and inserts. Build the presentation around compact packaging that still feels intentional. Healthy margins often come from disciplined packaging and bundle design, not from making the package physically large.

Giftable and Occasion-Based Products

Gift products can support higher perceived value because customers are buying presentation, convenience, and meaning at the same time. They also create seasonal opportunities, but you should keep a year-round core so the store is not dependent on a few holiday weeks.

19. Greeting Card Sets

Greeting cards are inexpensive to store and ship, but single-card orders can struggle with low order value. Sets solve that problem. Options include birthday bundles, thank-you packs, sympathy sets, or mixed “always have a card ready” boxes.

Design for a defined buyer. A corporate thank-you set should look and sound different from playful cards for close friends. The clearer the audience, the easier it becomes to write product descriptions and create future collections.

Paper quality, print accuracy, envelopes, and packaging influence perceived value heavily. Order test prints and inspect color, trimming, fold alignment, and how the cards survive mailing. If cards are blank inside, say so. If they contain messages, show enough preview information for customers to know what they are buying.

Once you find a popular style, you can increase average order value with larger packs or coordinated tags and note cards. Avoid producing too many occasion-specific designs before demand exists. A small evergreen collection gives you better information about what buyers want next.

20. Personalized Gift Boxes

Personalized gift boxes can create healthy order values because the customer is paying for curation and convenience, not only the cost of each item. Start with a narrow recipient or occasion, such as employee welcomes, bridesmaid gifts, teacher appreciation, or new-home gifts.

Keep the contents standardized. Unlimited “build anything you want” customization can turn every order into a manual sourcing project. A better model is one core box with two or three controlled choices, such as color, name, or message card.

Calculate margins at the box level. Include the contents, outer packaging, filler, personalization labor, payment fees, and shipping weight. Gift packaging can become surprisingly expensive, especially when decorative materials increase parcel size.

Also pay attention to the rules that apply to individual contents. If you include food, cosmetics, alcohol, or other regulated goods, compliance becomes more complicated. A beginner can reduce risk by starting with simple non-regulated items and focusing the personalization on packaging, stationery, or accessories.

21. Party Favor and Event Kits

Party favor kits work when they save the buyer time before a specific event. Create coordinated packs for birthdays, baby showers, weddings, classroom celebrations, or corporate gatherings.

The margin advantage comes from batching. You can prepare standardized components in sets of ten, twenty, or fifty while charging for convenience, theme consistency, and personalization. Keep the options controlled so production does not become chaotic as quantities rise.

Deadlines are the main operational risk. Your product page should explain order cutoffs, production time, what the buyer must submit, and whether proofs are included. Event customers have fixed dates, so a late order can create more dissatisfaction than a normal retail delay.

Choose components that pack efficiently and survive shipping. Flat tags, stickers, cards, small bags, and lightweight accessories are easier to manage than fragile containers. If one event theme becomes a bestseller, build adjacent products around it—such as invitations, thank-you cards, or digital signage—rather than launching a completely different event category.

Validate, Price, and Optimize Before You Scale

A good product idea is only a starting hypothesis. Your next job is to prove that real customers will pay enough for it, then improve the offer using order-level economics and customer behavior instead of expanding the catalog too quickly.

Validate Demand With Small Tests, Not Large Inventory

The safest first test is usually the smallest version that still looks like a real offer. For digital goods, launch one complete pack rather than ten. For handmade or personalized goods, use a limited batch or controlled number of order slots.

You can also test with a waitlist, preorder, limited drop, or landing page when appropriate. Observe behavior rather than compliments: signups, add-to-carts, completed orders, and repeated questions are more useful signals.

Track why people hesitate. If visitors ask whether a kit includes a certain component, your offer may feel incomplete. If they like the product but leave at shipping, the order value may be too low for the delivery cost.

Do not interpret one good day as proof of long-term demand. Run multiple small tests, especially if traffic came from a seasonal event or one viral post. You are looking for repeatable interest, workable economics, and consistently dependable fulfillment.

Price for Contribution Margin and Average Order Value

Pricing should begin with your cost structure and customer value, not with the lowest competing price you can find. Calculate the variable cost of one order, decide how much contribution you need, then evaluate whether the resulting price makes sense for your target buyer and positioning.

If a single item cannot support the required margin, change the offer before assuming the only solution is a price cut. Bundles, multipacks, personalization, premium materials, or a larger problem-solving kit can raise average order value without multiplying acquisition costs at the same rate.

A two-item bundle can offer a modest per-item saving while increasing total contribution, but the numbers should come from your own costs.

Also remember that free-store pricing does not mean zero selling cost. Payment processing, shipping, packaging, refunds, taxes, marketplace or app fees you add later, and customer acquisition can all matter. Review contribution margin by product and by order so a popular low-margin item does not hide the stronger products carrying the business.

Troubleshoot Weak Sales Before Blaming the Product

When a product does not sell, identify where the funnel breaks. Low traffic suggests a discovery problem. Product page visits without add-to-carts may point to weak positioning, pricing, photography, or unclear benefits. Add-to-carts without purchases can signal shipping surprises, trust concerns, checkout friction, or a mismatch between the advertised price and final total.

If buyers repeatedly misunderstand size, material, compatibility, or personalization, improve the listing before buying more traffic. Better images, dimensions, examples, and concise instructions can reduce costly mistakes.

Do not fix every problem by discounting. A lower price can increase conversion while making the business less sustainable. Sometimes the better move is to improve the bundle, narrow the audience, simplify options, or remove a weak product entirely.

I recommend reviewing a small set of metrics regularly: product page conversion, average order value, contribution per order, refund or return reasons, and repeat purchase behavior where relevant. Those numbers tell you whether to improve the page, the offer, or the product itself.

Choose a Product Your Economics Can Support

The best products to sell on a free online store give you room to learn without tying up too much cash. Digital files, personalized goods, print-on-demand products, lightweight accessories, small kits, and giftable bundles all share useful characteristics: they can be tested in limited quantities, differentiated for a niche, and improved without rebuilding the entire business.

Choose one idea that matches your skills, audience, and fulfillment capacity. Calculate the contribution margin before launch, create the smallest credible offer, and watch what customers actually do. If demand appears but the numbers are weak, improve pricing, bundling, or costs before scaling.

A free storefront can reduce startup pressure, but the product still has to earn its place. Start narrow, measure every order, and expand into adjacent products only after a winner proves repeatable demand and workable fulfillment.

Juxhin

I’m Juxhin, the voice behind The Justifiable.
I’ve spent 6+ years building blogs, managing affiliate campaigns, and testing the messy world of online business. Here, I cut the fluff and share the strategies that actually move the needle — so you can build income that’s sustainable, not speculative.

Related posts:

How Much Can An Ecommerce Store Make? Real Numbers And Profit Examples How Much Can An Ecommerce Website Make? Real Numbers Revealed Is Online Ecommerce Worth It For Beginners Or Too Risky To Start? Ecommerce Platform Realistic Income Expectations: What Sellers Can Expect Online Store Builder Review For Side Hustles: Can It Create Extra Income? Ecommerce Accounting Explained Simply: What Every New Seller Should Know