"How are we supposed to know before we put them on?"

I get seriously muddled with some of these discussions.

If Jim is saying that all *amateur session* members need to be vetted, then I say he is wrong. In the same way any amateur club accepts all-comers (be they watercolourists or macrameists).

If Jim is saying folk clubs aught to vet whatever they put up on stage before a *paying audience*, then I agree.