Related question: so what do you do if after a gig, they ask you to leave an invoice and they'll send you a cheque, and then a month later, no cheque has appeared?

How long would you wait before pursuing it? And would you call them, mail them another invoice, or what?

The specifics: it was for a gig at a nursing home party, we had a gentlewoman's agreement rather than a contract, and I made up a handwritten invoice there (not on an official invoice form or anything). One possibly complicating factor is that they originally told me that the party would be 1.5 to 2 hours long, and didn't mention booking any other entertainers, so I made up a price based on that. As it turned out, the party was less than an hour and there were other acts there so I only ended up playing about 20 minutes. But in my mind, since I showed up prepared to play for 2 hours as we had agreed, my price didn't go down.

Thanks, Marion