system
A chat on subreddit /r/pcmasterrace
human
I bought an ex-mining card a couple months ago. Palit gamerock 3070. So far haven't had any problems with it. The seller said it was used in a well air conditioned and dust free room and it was under volted. We agreed that the sale could be canceled if I find something wrong with the card so I was trusting enough to buy it. 

Currently used rtx 3070 are on sale for 500-550€ in my country, I happened to get this one for 450€ so I think I paid a good price. I haven't hit temps higher than 78°C yet, though this really depens on the case and fan configuration and gpu fan curve. Next up I'm searching information if I can replace all thermal pads and paste without voiding varranty, which this card happens to have for like a year still.

Personally, I wouldn't expect a gpu to run on good temps if you lock the fan speed to 40%...
gpt
All the miners say the same thing when trying to sell their cards.
Just like when you buy a car, they will say in the listing, lady owner non-smoking. Yet the person selling it is a fat hairy dude who looks like he smokes....