If you're charging the audience an admission fee, exercising a little quality control is a duty of care, rather than "unthinkable" behaviour! True, one of the great joys of Folk Club "open house" nights is that anyone can perform, and it's those nights that I operate a "come all ye" policy. On guest nights, I operate a far stricter system - basically I'll ask a good local performer/s to play a support set in exchange for free admission, and that's it. I've actually lost count of the number of people who've said to me that they went to __________ folk club/s to see a particular guest performer and had to sit through interminable awful floor singers, so won't go again in a hurry...