Assume as vendor your cost is $.07 cents per token and someone pays you $.25 cents for it.  You just made $.18 cents.  If the kid never plays the game you got $.18 cents and somebody else didn't have to wait for it.  If they brought in $5 worth of quarters they might or might not spend all of them.  If they had to change a $5 bill for tokens, then you get all their $5 when you might not have before.  If they don't spend all the tokens that day, then they will probably want to come back to use the left-over tokens and then they will probably buy more at that point.