Learn e-commerce, one card at a time
Flashcards on the fees, formulas and terms every online seller needs — plus in-depth guides and a seller glossary.
What is Amazon’s referral fee for most categories?
Tap to reveal the answer15% of the total sales price (including shipping charged to the buyer). Some categories are lower (electronics 8%) or tiered (clothing, jewelry).
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Go deeper with guides
Plain-English explainers for the numbers behind every tool.
Marketplace Fees · 6 min read
Amazon Seller Fees Explained (2026)
Every fee Amazon charges sellers in 2026 — referral fees by category, FBA, subscription and the extras — and how to work out your real profit per unit.
Marketplace Fees · 5 min read
Etsy Fees Explained (2026): What Etsy Takes From Every Sale
A clear breakdown of Etsy’s 2026 fees — listing, 6.5% transaction, payment processing and Offsite Ads — with a worked example and tips to protect your margin.
Payment Fees · 4 min read
PayPal Fees for Business (2026) — and How Much to Charge
PayPal’s 2026 business fees explained: Checkout vs goods & services rates, international fees, and the formula to charge the right amount.
Pricing & Profit · 5 min read
Profit Margin vs Markup: The Difference That Costs Sellers Money
Margin and markup explained with examples, a conversion table, and how to price products so you hit the margin you actually need.
Marketing & Ads · 5 min read
ACoS vs ROAS: What’s a Good Number for Your Ads?
ACoS and ROAS explained for Amazon, Walmart, Google and Meta sellers — how they relate, TACoS, and how to find your own break-even target.
Shipping & Logistics · 4 min read
Dimensional Weight Explained: Why Your Shipping Costs More Than It Should
How UPS, FedEx and USPS calculate dimensional weight, the divisors they use, and practical ways to cut your billable weight.
Marketplace Fees · 5 min read
eBay Fees Explained (2026): Final Value Fee, Per-Order Fee and Promoted Listings
How eBay’s 2026 seller fees work — the 13.6% final value fee, per-order fee, category rates and Promoted Listings — with a worked example.
Payment Fees · 4 min read
Stripe Fees Explained (2026): Card Rates, International Fees and How Much to Charge
Stripe’s 2026 US card fees explained — 2.9% + 30¢, international and currency conversion add-ons, refunds and disputes — with examples.
Payment Fees · 4 min read
Shopify Payments Fees and Transaction Fees Explained (2026)
What Shopify charges per order in 2026: Shopify Payments card rates by plan, in-person rates, and the extra fee for third-party payment gateways.
Shipping & Logistics · 5 min read
How to Calculate Landed Cost (With a Worked Example)
Calculate the true cost of imported products: product cost, freight, insurance, import duty and fees — plus why FOB vs CIF changes your duty.
Shipping & Logistics · 5 min read
Safety Stock and Reorder Point: When to Reorder Inventory
How to calculate safety stock and your reorder point from daily sales, sales variation and lead time — so you reorder before you run out.
Listing & Store Tools · 4 min read
Amazon Backend Search Terms: The 250-Byte Rule and How to Use It
How Amazon backend search terms work, why the limit is in bytes not characters, and what to include or leave out — with a cleanup example.
Seller terms, explained
From ACoS to Incoterms — short definitions with real examples.