There are some "dealers" that walk around Skyrim. Most of them try to kill me after we talk and I decline their offer because they're afraid I'll go tell the guards.
I saw one a few days ago that got killed by some thiefs, then I killed the thiefs - it was a good day for law enforcement lol.
Outside of Whiterun? I was working on the trophy for having 1000 bounty in each hold, and I killed some characters outside the walls right in front of a guard hoping that would get me my bounty, turns out the guards started helping me kill them. I thought maybe they were into bad things. Damn skooma junkies hangin out in front of the gates like a medievil jay and silent bob.