All Amazon.com sellers must pay referral fees, which vary by product listing, in addition to selling plan fees.

True is the correct answer because all Amazon.com sellers must pay referral fees, which vary by product category, in addition to the selling plan fees. Referral fees are a percentage of the product's sale price and are charged when a product is sold on Amazon. These fees are applied to all product listings and differ depending on the category of the product, such as electronics, clothing, or books. Referral fees are separate from the selling plan fees, which are the monthly fees associated with the seller's account (such as the Professional or Individual selling plan). The combination of referral fees and selling plan fees ensures that Amazon can provide its marketplace services while helping sellers reach a broad customer base.