British English has many phrases for favors that are expected to be repaid.
I owe you one: You did me a favor, and I will return it.
To return the favor: To repay a kindness.
One good turn deserves another: A favor should be repaid.
Mates’ rates: A lower price for a friend.
To call in a favor: To ask for repayment of an earlier kindness.
Sharp practice: Behavior that is legal but dishonest or unfair.