If you are someone who's into purchasing used graphic cards, you'll be mostly warned to avoid some specific GPU's, as they could be used for mining previously, most of those gpu's are specifically from AMD (There are some GPU's from Nvidia that were used a lot for mining, but they are few compared to the ones in AMD, such as 1070, 1060 6GB, and some 1080 & 1080Ti's), what do you think could be the reason ? is it because AMD GPU's are cheaper ? (atleast for now)