My biggest concern buying a used GPU is if it has been mined on..if so, its running conditions (hot, humid environment).
Also, when decommisioned and stripped out of the warehouse, how has it been handled, thrown into a box quickly with 100's of other gpus.
I bought 2 Radeon RX570 gpus sold as ex mining cards a few years ago, one had a broken left fan blade and the other had the right fan had sheared off its fans axis so neither card could be used until I took both apart and rebuilt a full working card from the good parts.
I got a full refund on one card and happily built the working one into a cheap gaming pc for a charity.
Both cards had corrosion buildup on the heatsink fins from being run in high humidity or salty location.
The BIOS were left at stock, so werent tweaked for mining, but thats a concern too.