When cash plays, what happens if there is Fake money?

[PhatPots]

Just a hypothetical situation, I was discussing this with someone else. I sometimes play in a 10/20 game, usually the majority of the money around the table is cash with some red $5 chips and a few green chips here and there.
When players sit down, they just buy chips from other players using $100 bills.

What would happen if a player were all-in loses the hand and the player winning the pot takes the stack of hundreds and notices that one or two of the bills is fake. Does the player with the fake money have to make up the difference?

What if a similar situation where several players have gone bust, money has changed hands several times and then a player makes a raise and sticks in $300 where one of the bills is fake. He obviously claims it is one of the players who busted a few hours ago. What happens?