I bought some used GPUs during the last mining thing. They all worked fine except for some oddball Dell models that the seller was obviously trying to fix a problem on (and they took them back without question, even paying return shipping).

And old mining GPUs are A-OK, generally: Despite warnings from the peanut gallery for over over a decade that mining ruins video cards, this has never really been the case. Profitable miners have always tended to treat these things very carefully, undervolt (and often, underclock) them, and pay attention to them so they could be run as cool and inexpensively as possible. Killing cards is bad for profits, so they aimed towards keeping them alive.

GPUs that were used for gaming are also OK, usually. They'll have fewer hours of hard[er] work on them, but will have more thermal cycles as gaming tends to be much more intermittent than continuous mining is.

The usual caveats apply as when buying anything else (used, "new", or whatever) from randos on teh Interwebz. (And fans eventually die, and so do thermal interfaces (pads and thermal compound), but those are all easily replaceable by anyone with a small toolkit and half a brain worth of wit.)