I usually give something (if times get hard I might be on the other end) - depends what's in my pocket; if I stood and listened for a while I'd expect to give accordingly, but I don't always get the chance to hang around.

I saw a guy once in Sutton Coldfield (England) playing a trumpet to backing tapes. He was very good - souded just like General Lafayette (or if you're too old, Eddie Cantor). I stood and watched him a while - from a distance - and began to get suspicious. I don't expect all trumpeters' cheeks to inflate like Dizzy Gillespie's, but I do expect them to look as if they're breathing - this guy's cheeks never even fluttered! I didn't have the nerve to walk up close and make sure if he was miming.

Steve