A friend of mine is notoriously bad at paying out his losing bets and I've had to "chase" him for months several times to close his bets with me (a few hundred bucks and he can definitely afford it).  Finally, pay back presents itself.  He's the banker and co-organizer for a bachelor party we are organizing for a common friend.  He's put down deposits and requested people send him cash so he's not out of pocket for long.  We're talking about $2000 USD total for the week per person.  No problem, I look at the breakdown of costs to make sure I'm not overpaying as I don't want him to owe me money at the end of it as I suspect it's going to be a bitch to get it back from him.  I notice that they overcharged me $150, innocent mistake, I bring it to their attention and they tell me, np just pay us $1850.  I send it.  Incidentally right after I send payment, the other organizer says that the amount was for contingency / incidentals, but no big deal we'll just settle at the end.  A few days later, he brings the subject up again saying it's not fair to the group that I didn't pay the extra $150.  I explain that he said it was fine and I also let him know that the banker has been a notoriously slow payer to me and I don't want to have a balance owed to me by him by the end of this.  He disagrees as my issue with my friend has nothing to do with the group (which I don't think makes any sense since a balance will likely be owed one way or another).  AITA for withholding the $150?