A very tiny fraction. But I have to assume that most criminals on there would be smart enough not to reach out to the FBI unless they were facing far worse trouble than the possibility of being charged with a crime for this. I could be wrong, there could be criminals dumb enough to expose themselves to prosecution — they are criminals after all — but I would expect them to be smarter than the average street criminal.

Most of those vendors would flip and cooperate once pressed even a tiny bit by law enforcement. They're probably just regular ole nerds who made money in a bad and stupid way.

I mean, I've gone to websites similar to this in the past, after seeing them mentioned on sites like Krebs, simply out of sheer curiosity (as mentioned elsewhere in the thread, a lot of my curiosity stemmed from a place of, "Hold on, this sort of site is publicly hosted and easily available to anyone!? I can't believe that"). I've never registered or posted, but some of those sites/forums are wide open for the public to peruse. I'm not even that technologically savvy or into security research, yet I've made it there, so I imagine the number is a bit higher than you'd expect.