From Longman Dictionary of Contemporary Englishfair enoughfair enoughespecially British English used to say that you agree with someone’s suggestion or that something seems reasonable SYN OK ‘I think we should split the bill.’ ‘Fair enough.’ → fair
Examples from the Corpus
fair enough• "I'll trade you my tennis racket for your skates." "Okay, fair enough."• But, you know, that's fair enough.• Cuntonas rating is also fair enough.• If it's in your blood, your ancestry, then I think that is fair enough.• Its results can be fair enough.• This is fair enough, but do check before you buy.• Which was fair enough comment at the time.• And the price you paid seems to be fair enough - even taking the bad news into account.• However, it seemed fair enough to start the climb in the hope of an improvement. 