There are many fulfillment fees when you are selling on Amazon. One of is referral fee.
Sellers pay a referral fee for each item sold. Items in several categories have a per-item minimum referral fee as listed below (for example, sellers pay the greater of the referral fee or the per-item minimum referral fee).
For all products, Amazon deducts the applicable referral fee percentage calculated on the total sales price, excluding any taxes calculated through Amazon tax calculation services. The total sales price is the total amount paid by the buyer, including the item price and any delivery or gift wrapping charges.
Referral fees vary by category, as listed below.