What is the Amazon referral fee?

Amazon's commission on every sale, charged as a percentage of the price.

The referral fee is Amazon's commission for the sale itself - a percentage of the total sale price, charged on every order whether you fulfil with FBA or yourself. The percentage depends on the category; for most categories it sits around fifteen percent, with published exceptions above and below.

It is the first number to subtract when pricing a flip, and the one beginners forget most often. Rather than memorising category tables that Amazon updates, price the actual product: a deal calculator applies the current referral and fulfilment fees and shows the margin that is actually left.