Definition (原则)
This phrase is used to indicate that someone should behave reasonably or treat others the same way they are treated.
公平交易；应该公平待人
Okay, it's my turn now. Fair's fair.
好吧，现在轮到我了。公平就是公平。
I don't usually like this kind of music, but fair's fair, this song is really good.
我通常不喜欢这种音乐，但公平就是公平，这首歌真的很好听。
If he can have time off, then so should I. Fair's fair.
如果他能休假，那我也应该可以。公平就是公平。