>>If sufficient people don't turn up, that's not the failure of the performer, but rather of the club organiser who made the booking in the first place, and who was in a better position to know who might draw in people, and to do the things that might help in ensuring that.
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Couldn't agree with you more MoH

I must say though, its bloody difficult turning a performer down when you know they are very good, but doubt they will attract enough bums on seats for the style of club that you run.
This is where honesty comes in. If the performer is not what you are looking for - tell them and tell them why. You are not being rude to them. I think theer is nothing worse than a performer playing at a club, that is not suitable for what they do. That is the organisers job to explain the style of club and if you think no, then say no.