> Are you claiming that it is somehow unsafe to use?

For your wallet, yes. Do you have any information about the environment in which a card was used? Temperature, dust, air moisture were like in a home or there operated in an industrial warehouse? Fan bearing status after all these hours? Voltage applied? Stock BIOS? were they in an enclosure or in a sort of a case? Thermal paste has been changed? Ever been disassembled?

I would not trust a miner's card even if it was a gift.

Miners screwed the market over and now they want you to think that their used crap is such a bargain. Let them deal with their waste, don't help them.