Don't see a way to confirm a card hasn't been used for mining, but if you're using something like ebay which lets you see the person's selling history you may be able to sus out if they are more likely than not mining cards. Someone who has a listing for multiple cards for sale, or has a history of selling a bunch of GPUs of the same type or same generation may be a giveaway.
It may be counterintuitive, and I may very well be wrong, but I would reckon used 3000 series cards are less likely to have been used for mining than older gens on the market. The new cards are still more than profitable at this point, Ethereum mining difficulty may be growing but so is its price. Ethereum also has more optimistic price predictions which will likely keep people mining it throughout this year rather than selling due to the typical crypto price fluctuations that happen fairly often. Will take the big crash to get a massive dump on the used market from miners who have thrown in the towel.
I suspect people who are selling "used" current gen cards are mainly people who due to the current crunch couldn't get the card they wanted and had to settle on something else. After finally being able to pick up what they actually wanted, they list the "old" card on ebay or whatever. At least this is what happened to me. Really wanted a 3090 but was able to get lucky enough and find a 3080 at Microcenter back in November. Finally got lucky with an EVGA queue order for a 3090 in late December and sold the 3080 to a friend. If I was smart I would have used the 3080 as a miner, but back then I would have probably just listed it on ebay if I didn't have a private sale.
Buyer beware however, and as it's been said, it may be fair to assume any card listed for sale used has been used for mining at some point.
It may be counterintuitive, and I may very well be wrong, but I would reckon used 3000 series cards are less likely to have been used for mining than older gens on the market. The new cards are still more than profitable at this point, Ethereum mining difficulty may be growing but so is its price. Ethereum also has more optimistic price predictions which will likely keep people mining it throughout this year rather than selling due to the typical crypto price fluctuations that happen fairly often. Will take the big crash to get a massive dump on the used market from miners who have thrown in the towel.
I suspect people who are selling "used" current gen cards are mainly people who due to the current crunch couldn't get the card they wanted and had to settle on something else. After finally being able to pick up what they actually wanted, they list the "old" card on ebay or whatever. At least this is what happened to me. Really wanted a 3090 but was able to get lucky enough and find a 3080 at Microcenter back in November. Finally got lucky with an EVGA queue order for a 3090 in late December and sold the 3080 to a friend. If I was smart I would have used the 3080 as a miner, but back then I would have probably just listed it on ebay if I didn't have a private sale.
Buyer beware however, and as it's been said, it may be fair to assume any card listed for sale used has been used for mining at some point.