<p>When he contacts you, express your concern for the person who's ill, and ask how he would like to take care of the balance due for the evening. In the future, to give yourself some protection, tell folks you have a minimum and get that up front. Or figure out that you'll be working at least x number of hours, get paid for that in advance, and then settle up the night of, or the next day. Keep it business-like, yet personal. Otherwise, you're working for free.</p>