Ah, I see. Yes, you're right, they do manufacture reference design cards. First time dealing with reference models, since those aren't sold where I live, hence the confusion, haha
Those will all be the same in terms of temperature and clock speeds. Build quality should only vary insignificantly, although I do not trust Gigabyte, due to 3000 series PCB issues and how they handled it, and ASUS due to their borderline scam customer support.
You won't be getting any warranty buying used, I don't think. So, imo, just get the cheapest one. You should concern yourself more with the seller, and do make sure to thoroughly check everything after buying. Both physically and performance-wise.
Surprised nobody said cell degradation.
You now can live for as long as you're not killed whilst physically keeping an appearance of an ~30 y.o. This also technically prevents cancer.