I Don't Buy It

Whenever I read about gun buy back programs, I have to wonder what's the point? They're trying to "get guns of the streets," but what sort of person returns a gun? That's not rhetorical, I honestly don't know. Is there a profile for the kind of person who's involved? Are there people ready to commit crimes that give back their guns? And do they offer enough to make it worthwhile, or would it be better to try a pawnshop? Is this a chance for people to go around "finding" stray guns so they can make some quick cash, like a bigger version of returning empties?

And is there any evidence, shaky or otherwise, that these programs effect local crime in any way?