Current source backbone
Google Search Central documentation
Google AdSense Help and Publisher Policies
PayPal Business Fees
Stripe Pricing
Etsy Fees and Payments Policy
Amazon Seller Pricing
Shopify official company and commerce pages
SellerGauge
Sources
SellerGauge uses official or primary-source documentation wherever possible for rates, platform fees, and tax references.
Source handling
If a page uses a simplified assumption for speed, that assumption should be labeled and linked to the closest official source available.