k3 caps are pretty off from what i've seen. the colors and textures don't look right at all. so probably no worries unless you really have no clue.
there are a lot of fakes from the last couple of years. the ones i've seen are single colors (including translucents), drunken, and candy corn. i would avoid all of those. even reputable people have unknowingly picked them up, so don't just go by the previous owner. you need to know the full ownership history or find someone who had the clacks from a long time ago.
i've heard of other fufu like OG tri and OG night owl, but i don't remember seeing photos of them so i don't know how good or bad they are.
i'm guessing the recent shiny eyed skulls and any with the 3 dots should probably be ok.
nowadays, people are throwing stupid amounts of money at people with throwaway accounts, and not doing much research either. it's pretty dumb.