How FlipCalc verifies marketplace seller fees
FlipCalc uses official marketplace fee documentation as the source of truth, then keeps the fee engine, explanation copy, structured data, and generated pages aligned before updates are treated as ready to publish.
Official fee pages come first
Each supported marketplace starts with its official fee page, help center article, or fee policy. FlipCalc does not use forum posts, seller anecdotes, or scraped competitor calculators as the primary source for fee rates.
When a platform has multiple seller costs, the calculator models the core fees that affect pre-listing profit decisions. Optional ads, discounts, refunds, tax treatment, international rules, and account-specific promotions are called out as limits when they are not part of the core model.
eBay
Category-based final value fees plus per-order fee
Verified April 30, 2026
Etsy
Transaction fee, listing fee, and payment processing fee
Verified April 30, 2026
Poshmark
Flat low-price fee or percentage selling fee
Verified April 30, 2026
Mercari
Flat seller fee on item price plus buyer-paid shipping
Verified April 30, 2026
Depop
Payment processing fee with no US selling commission
Verified April 30, 2026
Facebook Marketplace
Fee-free local pickup or 10% shipped checkout fee
Verified May 1, 2026
StockX
Seller-level transaction fee plus payment processing
Verified May 1, 2026
Whatnot
Category commission plus payment processing
Verified May 1, 2026
Amazon
Category referral fee plus selling plan and fulfillment costs
Verified May 1, 2026
What gets calculated
The calculator starts with sale price and buyer-paid shipping, applies the marketplace fee model, then subtracts seller shipping cost, item cost, and optional promotion cost where the platform supports that input.
Category pages use the same fee engine as the main calculator page. When a marketplace has category-specific fees, the generated page and calculator both read from the same platform configuration instead of maintaining a second copy of the math in page text.
How often fees are reviewed
Core fee sources are reviewed at least monthly, and sooner when a marketplace announces a fee change. Visible badges on calculator and comparison pages show the most recent verification month.
A fee update is complete only after the source reference, calculator configuration, public explanation copy, tests, production build, and SEO audit have all been checked in the same pass.
Recent verification history
April 30, 2026
Public verification badges added
Calculator and comparison pages now show a visible last-verified badge that points back to this methodology page.
May 1, 2026
Official source review completed
The current eBay, Etsy, Poshmark, Mercari, Depop, Facebook Marketplace, StockX, Whatnot, Amazon, and Grailed fee assumptions were checked against each platform source listed below.
March 15, 2026
Calculator review workflow documented
The public About page was updated to explain how fee references, calculator config, explanation copy, tests, and production builds stay aligned.
Who maintains the calculator data
Maciej Dudziak builds and maintains FlipCalc through Maciej Dudziak IT Services in Poland for marketplace sellers who want clear fee math, current fee notes, and practical pricing guidance before they list an item.
FlipCalc is operated by Maciej Dudziak IT Services in Poland. For fee corrections, source updates, or calculator edge cases, contact maciejdzk@gmail.com.