All is fair in tennis and beer purchasing

A well-known saying that has been used to describe instances of tennis/beer-related activities since the early 1700’s.

Person 1: I can’t remember how much more beer I owe you for our tennis games.
Person 2: somewhere between $9 and $5 million dollars.
Person 1: that doesn’t seem fair

Person 2: All is fair in tennis and beer purchasing. That’s the saying.