There's a very good chance that GPU you bought second-hand from some desperate erstwhile crypto miner will work fine. Mining ethereum 24 hours a day doesn't actually put a lot of undue stress on the graphics silicon, particularly as a lot of them will be underclocked to reduce the power draw.
That doesn't mean the graphics card as a whole will work fine, however, because what cryptocurrency mining does seem to chew through are the memory chips attached to your GPU. Those could get fried, then be bypassed by an enterprising miner, and the whole card would still limp along as a shadow of its former self.
Caveat emptor. Buyer beware. That's the general jist around whether you should take advantage of the latest cryptocurrency crash and buy yourself a cheap second-hand GPU that's been stuck down the crypto mines for the past two years.
Yeah, I got legal latin chops, what of it?
There's a piece on WCCFTech that goes into the story of one user who bought themselves an MSI RTX 3080 card for around half the current retail price of the card in the US, only to find that 2GB of its memory was burnt out. With the Asian GPU market getting flooded by second-hand cards, as miners seek to ship off their inventory while they might still be able to recoup some of their investment in hardware, this could become a common story.
The piece notes there are bypasses available, which allow miners to get around bust memory chips on a board and still allow them to use a graphics card, albeit at reduced effectiveness, using the remaining functional chips. It is apparently called 'memory shielding,' though is beyond my personal ken.
You could, if you had ready access to identical memory chips, have the broken ones replaced and your used card would once more be ready to roll at full chat. But that's a niche case, and more likely you'll just be left with a lame card.
The second-hand market is definitely going to be buoyed—across the globe—by the crypto crash, but that doesn't necessarily make it a great time to grab a used GPU. In truth, probably the opposite.
Our advice would be to steer clear of any second-hand GPU you suspect has been used for mining, and if at all possible see it working before you part with your hard earned cash.