>>64242896 (OP)
Used revolvers are a minefield, only buy them if you know what you're doing and what you're looking for. It's relatively easy for one to be slightly mistimed or have a tiny bend in the frame that makes it shoot like shit.
For most other guns you just need to check basic mechanical function (including the safety and firing pin) and make sure there's no damage to the bore/chamber. Bring a light, some snap-caps, and do a little research on the guns you know you might want to buy beforehand to understand what the most common issues are. For older rifles, a headspacing gauge is a good idea as well. If a store won't let you check the weapon before you buy it, they're not someone you should be buying guns from. Be prepared to see something you're interested in, go home and do some research, and come back for it later. It might not be there, but it's better to have nothing than a lemon you can't fix and trying to unload it on the next sucker. If you're lucky the store will have a gunsmith on-site who inspects all their used hardware, but that's gotten a lot rarer these days.
For what it's worth, I've gotten more than half my guns used. Some of them were broken in easily-repaired ways (springs or poor maintenance), so I verified it and used that to negotiate the price down. Then I could do the basic repairs they required to get them back online again.
