One bit of advice - when you give a performer a specific number of songs do make them understand that PART of a song counts as a song. There's been many occasions where I've heard a singer forget the words over halfway through a song and then start a new one - they often seem to think that they can keep going until they actually manage to complete one !

When I ran a Folk Club, I would only give any unknown floorspot performer(s) one song to start with. If they were up to scratch they got more.

There are usually many sessions where less-talented or inexperienced performers can improve their skills - we all had to start somewhere, but if you are charging an admission fee or receiving payment for the entertainment, then you must set a minimum standard.