"Professional" in as much as he/she is good enough, competent enough and entertaining enough to actually be able to make their living from doing something that they obviously love. Not all "Guests" booked will be regarded by the entire audience as being the bees-knees, different strokes for different folks, but in general a professional performer is someone that can teach us amateurs a thing or two.

Oh by the way Jack, it is the fault of the so-called "Folk Clubs" that have allowed anything to be played that this "tradition" that you are on about (And obviously care about as do both Jim Carroll and myself) has become so diluted as to now be almost irrelevant.

"People who sing usually believe the(y) can sing."

Of course they do, and many of those you go on to describe probably think so because they have read their way through a crib sheet and received the "sympathy-thank-f**k-that's-over" applause at some singaround.