Imagine the scenario:

A high profile guest has been booked who is expected to draw in a capacity audience.

A five piece folk band, who you know to be very proficient but who you haven't seen at the club since at least a year ago, turn up wanting one of the three or four floor slots you have available. You know that they have probably come because they know there will be a large audience courtesy of the main guest's reputation, and they might sell a few CDs, get bookings, but you also know you probably won't see them again until you get another popular guest night.

One of the regulars who comes to the singaround every week also asks about a slot. They probably come into the "took years of practice to get this crap" bracket, but they are a loyal follower of the club, who perhaps helps with raffle, organisation ,etc.

I know guests often appreciate good warm up acts, but it's not easy, is it?

Sounds a bit like one of those scenarios they give you on training days doesn't it?

One of our local festivals has a final singaround when the preference for slots is given to the Stewards who have worked at the festival. I can't really see any problem in this.