I'm thinking that maybe they should pass out chits with the performers listed on them. Then there's a rating system:

"I thought this performer was excellent and would love to see this person again."

"I thought this performer was pretty good and wouldn't mind seeing this person again."

"I thought this performer was okay and could take this person or leave him/her."

"I didn't care for this performer but others might like him/her."

"I thought this was the performer from hell who couldn't carry a tune on a stretcher which is what it will need when s/he's done bollocks it up and I never want to even think of this person again much less him/her perform."

Now anyone can have an off-night so you get three chances to strut your stuff but if you get a stinko rating consistently, adios. Make sure every artist understands this going in and that it is the audience who decides not the establishment or the host. So if you get barred from performing there--blame yourself for blowing donkey balls. It won't stop crappy acts from showing up but it will keep them from returning.

I doubt people would be mean about it. A new act or a nervous act would likely get a pass. But a crappy or annoying act would get the heave-ho and, let's face it, if people don't want to see him then why should they see him?