Best thing to do is meet with em. Get a feel for who they are and hang out for awhile. Jam a few tunes and get feelf for how good they are.
I can't count the amount of times I've turned down a band cause of things like the band having crappy equipment, or a loudmouth in the band or even worse... a guy who can't play.
Figure on the fact that you'll be meeting with these guys several times a week, so can ya stand putting up with em.