How to check marketplace fee sources
A simple research discipline for sellers who do not want old fee assumptions quietly steering pricing.
Use official sources first
Marketplace fee pages, seller help centres and pricing documents should be the first source. Blog posts and forum answers can help explain context, but they should not be the source of truth.
If a fee cannot be verified, mark it as uncertain rather than burying it in the calculator.
Record the date
A fee value without a review date becomes stale quietly. The date tells future you whether the number deserves trust.
For production calculators, source URL, effective date and last reviewed date should travel with the fee rule.
Capture ambiguity
Some fees vary by category, country, seller type, fulfilment method or price band. A good model names that ambiguity.
It is better to show a scenario honestly than to pretend one blended fee covers every seller.