I would expect the organizers to be open about it, whether they will pay or not. Because my band, The Redemption Concept, requires much more than a rock band would since we do progressive rock. A lot more arrangement creativity required to create our originals, so we should at least get an idea of how we are to be paid if we are gonna be paid at all.
But, we're not an established band just yet, so no big payment for now. But, for performing and entertaining a crowd in a bar or something, I'd expect some payment at least. Charity shows are another thing: if they're going to give the proceeds to the SPCA or an orphanage or for a good cause, I'd expect them to pay, not to us, but to charity. I would take no payment for a charity show.
But, if we're entertaining people for the sake of entertainment, we should be paid, since we take the time to reserve the date, the transportation, etc. More so if we're using our own gear and the place only provides the sound system and the drums.