I don’t think it really matters how long it was used. Would you buy an 6 month old GPU that was inside a poorly ventilated case where the gamer overvolted and overclocked and gamed for like 4 hours a day? Or would you get it from a miner who undervolted it and had it in an open air rig.
The only issue with mining rigs are the fans. They generally wear out much quicker than some gamer. Since gamers generally only play 1-2 hours a day, usually the fan doesn’t spin at all during that time. Compared to a miner rig which had it running 60-70% fan speed for years.
What a world, I am a PC gamer and also a crypto miner myself maybe that's why I understand so many things that many don't about PC parts and gaming, I use a high end PC for gaming and I always leave the case opened, closing the case makes the GPU go hotter and I don't like it, if I am only a gamer I may find closing the case a better solution. . .