I've had people wander over and start flapping their gums about this or that, I typically won't stop what I'm doing, I'll just keep loading mags or whatever. If I'm getting ready to shoot, I'll let them know to put their ears on and let er rip. That usually gets them to move along.
I have had people offer to let me shoot their guns, which always seems kinda weird. The only time I took someone up on it was a guy that I kinda knew, and only because it was a Barrett .50 BMG. He's a local guy that owns an HVAC company and well known and respected. I walked over just to talk to him about it because it was unique and not something I'll ever own, and he asked me if I'd like to shoot it. He had me send 5 rounds down range, knowing what they cost I offered him a $20 bill that he refused. I jokingly offered to let him shoot my AK, which I thought he'd not be interested in. Turns out he'd never shot an AK and took me up on it. The smile on his face and the smile on mine were similar.
As far as people asking to shoot my guns, the answer would be no every time unless they're with me. I'd never ask to shoot someone else's guns whom I didn't know so it seems odd that people do that.