From Longman Dictionary of Contemporary Englishfair’s fairfair’s fairused when you think it is fair that someone should do something, especially because of something that has happenedearlierCome on, fair’s fair – I paid last time so it’s your turn. →fair
Examples from the Corpus
fair’s fair• Come on, fair's fair - I paid last time, so it's your turn.• Come on, fair's fair. It's your turn to mind the kids.