I've bought a lot of used guns. Mostly because they were interesting in one way or an other. FN FAL, UZI, AK's, P03 Lugar, Heckler and Kock pistols, and many more. Some were complete wrecks and I rebuilt them. Others were like new. Only one blew up on me. (no damage to me or anyone else, the steel just gave up)
A lot of times I bought guns just to see how they worked and if they were any good. I've kept the ones I liked.
Worst gun on the list above: The P03 Lugar. Not very practical and always dangerous when loaded. OK to look at, just don't try to carry one.