Everything I've seen for a while has involved gift cards, which aren't usually directly convertible to cash. Though I know there was an Illinois group in the not too distant past that managed to cash in some crap guns to buy decent stuff for a shooting camp.
And they should be called "buy-ups". "Cash 4 Clunkers".
So, I get gift cards for something I need, use the cash I would have used to buy that to buy a gun.
Hell, I'm not picky. Even if I don't use it to buy a gun, dear old Bloomy would still be giving money away too someone who openly thinks he's a moron.