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.
Which URLs should be cited for fee data
The Fee Index and Fee Changes tracker are generated from the same reviewed source data and calculator engine described on this page. Use the HTML pages for human readers, CSV for spreadsheet citations, JSON for machine-readable fee data, and RSS when monitoring marketplace fee updates. Seller reports summarize those data assets into dated editorial findings, while the embed page lets publishers pair those sources with an on-page calculator.
When citing FlipCalc, use the most specific URL that supports the claim: Fee Index for cross-marketplace fee comparisons, Fee Changes for historical updates, Seller Reports for quarterly or annual narrative summaries, the Embed Widget for publisher resource pages, the Publisher Kit for outreach-ready copy, Publisher Kit JSON for machine-readable asset discovery, the target and tracker CSVs for outreach planning, and platform calculator pages for exact current sale-price calculations.
Human-readable same-input fee and payout table across supported marketplaces.
Flat spreadsheet-friendly fee dataset generated from the production fee engine.
Machine-readable version of the same fee index data and assumptions.
Human-readable current seller fee formulas, source dates, and common price rows.
Machine-readable seller fee formulas and common sale-price rows by marketplace.
Spreadsheet-friendly seller fee formula and common price rows.
Sourced fee-change history with dates, before/after notes, and $50-sale impact.
Machine-readable fee-change events for analysis and citation.
RSS feed for publishers and crawlers monitoring marketplace fee changes.
Index of citable quarterly and annual report summaries built from the data assets.
Editorial summary layer for Q1 fee findings, source rows, and fee-change events.
Machine-readable report findings, source datasets, assumptions, and fee-change rows.
Spreadsheet-friendly report finding rows and fee-change rows.
Embeddable marketplace fee calculators for publishers who cite FlipCalc data.
Outreach-ready package of fee data links, embed guidance, and publisher copy.
Machine-readable manifest of citable assets, feeds, reports, embed guidance, and outreach files.
Machine-readable index of publisher-facing JSON, CSV, and RSS feeds.
Spreadsheet-friendly index of publisher-facing assets, feed URLs, formats, and use cases.
Copy-paste iframe and lazy-script examples for embedding FlipCalc calculators in articles.
Machine-readable lazy-load, sizing, attribution, and source-pairing guidance for embeds.
Machine-readable attribution and citation rules for publisher embeds and data reuse.
Machine-readable copy-paste source notes for fee data, reports, and widget attribution.
Machine-readable placement playbook for page types, source assets, widget positions, and tracking steps.
Machine-readable initial and follow-up messages for pitching FlipCalc data assets and widgets.
Machine-readable workflow connecting source assets, placements, pitch copy, and follow-up tracking.
HTML target list with publisher priorities, outreach angles, and source assets.
Downloadable tier-one target list for reseller publisher outreach planning.
Machine-readable tier-one target list for outreach planning and enrichment.
Spreadsheet template for tracking publisher targets, status, follow-ups, and results.
Recent verification history
May 16, 2026
Seller fees formula feeds documented
The Seller Fees JSON and CSV feeds were added to the public data asset list so publishers, crawlers, and AI systems can cite current platform fee formulas, source dates, and common sale-price rows.
May 15, 2026
Q1 reseller report CSV feed documented
The Q1 Reseller Fee Report CSV feed was added to the public data asset list so publishers, crawlers, and AI systems can find spreadsheet-friendly report findings and fee-change rows.
May 14, 2026
Q1 reseller report JSON feed documented
The Q1 Reseller Fee Report JSON feed was added to the public data asset list so publishers, crawlers, and AI systems can reuse report findings, source dataset links, assumptions, and fee-change rows.
May 14, 2026
Publisher attribution guidelines feed documented
The Publisher Attribution Guidelines JSON feed was added to the public data asset list so publishers can cite FlipCalc data and embed widgets with consistent attribution language.
May 14, 2026
Publisher outreach workflow feed documented
The Publisher Outreach Workflow JSON feed was added to the public data asset list so publishers can connect source assets, placement guidance, pitch copy, and follow-up tracking.
May 14, 2026
Publisher performance notes feed documented
The Publisher Performance Notes JSON feed was added to the public data asset list so publishers can review lazy-load, sizing, attribution, and source-pairing guidance for calculator embeds.
May 14, 2026
Publisher embed snippets feed documented
The Publisher Embed Snippets JSON feed was added to the public data asset list so publishers can find copy-paste iframe and lazy-script widget examples.
May 13, 2026
Publisher assets CSV documented
The Publisher Assets CSV index was added to the public data asset list so publisher teams can review FlipCalc source assets and feed URLs in a spreadsheet.
May 13, 2026
Publisher feeds index documented
The Publisher Feeds Index JSON feed was added to the public data asset list so publishers, crawlers, and AI systems can discover every publisher-facing JSON, CSV, and RSS feed from one URL.
May 13, 2026
Publisher outreach copy feed documented
The Publisher Outreach Copy JSON feed was added to the public data asset list so publishers and crawlers can reuse the initial and follow-up outreach messages from the publisher kit.
May 13, 2026
Publisher placement feed documented
The Publisher Placements JSON feed was added to the public data asset list so publishers and crawlers can match article types to source assets, widget positions, and outreach tracking actions.
May 13, 2026
Publisher citation feed documented
The Publisher Citation Snippets JSON feed was added to the public data asset list so publishers and AI systems can reuse exact source wording for Fee Index, fee-change, report, and widget citations.
May 12, 2026
Publisher manifest documented
The Publisher Kit JSON manifest was added to the methodology page and data navigation so publishers, crawlers, and AI systems can discover FlipCalc source assets from one machine-readable URL.
May 8, 2026
Public data assets and reports documented
The Fee Index CSV/JSON dataset, Fee Changes JSON/RSS feeds, and reseller reports were added to the methodology page so publishers and AI systems can cite the specific data URL behind a fee claim.
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.