If someone asks, I size them up (judge them, if you will), and make a decision. If he seems like a fairly professional person and convinces me he knows what he's doing, then yeah, he gets to play through my rig. I wouldn't let anyone play any of my boutique basses, with the exception of James East, who played my Drozd. The Fenders, maybe. First indication of impending damage to anything, and I'm on stage correcting the situation.
Now, if he's a she, no problem.
Now, if he's a she, no problem.