Doug,
The guy should have paid you the twenty, but you should ask him to pay it. That is the problem with lots of agents and bookies they are afraid of hurting someones feelings by asking them to pay their debt. If i never asked people that owe me to pay, i'd live in a dumpster. Only really solid people and people in the business will pay or offer to pay without being asked.
Kinda like selling, if you don't ask them for the order 9/10 times you won't get it.
Ask him to pay you the $20 if he does not pay you that day or the next then you can call him a turd.