And then you have repacks.

It's basically impossible to find any game that isn't on GOG that is not shared as a repack. You don't get the installer, you don't get the original media, you have to trust that the repack is not filled with malware. (and also the repack process somewhat confuses wine/lutris. More than once i couldn't make the repack run on my linux box, but if i managed to find the genuine install medium.. or if i ended up buying the game on sale, then no problem)