Since you asked - Aberdeen Folk Club stopped booking professional guests 2 years ago. I only went once last year, to hear Jimmy Crowley, whom I had booked at the club in the mid-1980s. On that occasion, Jimmy was a duo with the late Chris Twomey [RIP]. Although it was their first appearance in Aberdeen, the publicity was done right and there was a near capacity audience of over 100. They were paid a professional fee according to the rates at the time, and I think even got an increase on a "percentage of the door takings basis".
Jimmy was over last year to play at the Portsoy Festival - [ the "Haal", not the boat festival ], and had a night off beforehand in Aberdeen. Although it was short notice he could have been given a gig in my opinion. He was invited to be a "special guest" at a "Singers & Musicians" session. They "passed the hat" round for him, which I thought was extremely insulting to a professional and long established touring musician. Jimmy's choice, of course, and it was actually a very good evening. Audience was less than 50.
Not the mark of a "great" folk club, IMHO, of course.