Jack, it all depends on the type of club, or perhaps even the nature of that particular event, since many clubs operate both singers nights and guest nights. If it's a singers' night, singaround, open mic, come-all-ye, call it what you will, then it should be open to all-comers, with the risk that some of them may not be of very high standard - but if the atmosphere of the club is right that may not matter. If it's a concert night then being asked to perform, whether as a paid guest or a floorspot, should be seen as a privilege, not a right.

It's also important that the club is correctly publicised, so that the audience doesn't have mistaken expectations of what is on offer.