Referral fees are a common practice in the referral marketing industry. It's a way for networks to incentivize their users into referring more customers. There are two common structures for referral fees: percentage based and fixed fee.
Percentage based refers to a percentage of the customer’s first purchase, while fixed fee refers to a flat amount that is paid by the customer, regardless of what they buy.
The fixed fee structure can be better because it ensures that you get something from your referrals no matter what they buy, but you also have less incentive to refer more people than with the percentage.