Documented system
Methodology
How fee data is sourced, verified, version-controlled, and translated into impact estimates. Maintained as a public transparency resource for marketplace sellers.
Where data comes from
Every fee record is sourced directly from a marketplace's public seller help center: Amazon Seller Central, Walmart Seller Help, and Shopify's pricing pages. Each record stores the canonical source URL and the human-readable source title. We do not scrape third-party blogs or community posts — only first-party documentation issued by the marketplace itself.
How often it's verified
Records carry a last_verified date. We re-open the canonical source on a rolling cadence — at minimum quarterly, and within five business days of a marketplace fee announcement. When the published value still matches, we update last_verified. When the value has changed, we open a new version (see below).
How fee changes are tracked
When a marketplace publishes a new fee, the previous value is preserved in the fee_changes table with old_value, new_value, effective_date, and announcement_date. The active record in fee_records is updated to the new value. This means the database carries a complete version history and every change is auditable to its source URL.
How impact is estimated
Per-record percentage impact is calculated as (new_value − old_value) / old_value. Impact level (low / medium / high) is assigned editorially based on per-unit dollar delta and the share of typical sellers affected, using publicly reported category-mix data. Estimated seller impact figures published in long-form Impact Reports cite their methodology and sample size inline.
Public, programmatic access
The same data powering this site is exposed at /api/public/fees, /api/public/fee-changes, and /api/public/marketplaces as JSON. Endpoints are read-only and unauthenticated, intended for researchers, journalists, and seller tooling. Every JSON record includes its source_url so third parties can independently verify any value.
Methodology last reviewed June 2026. Corrections welcome — every record links back to its original public source.