If these were black market deals, how did the researchers know about them?
Because the kids told them?
And they believed the kids were telling the truth?
You might enjoy reading Gang Leader For A Day, written by a grad student who first stidoed, and then earned the trust of some inner city gang members, so much so that a gang leader offered him to run the gang for a day. I found it a fascinating read. Funny story, the author is Indian, so he wasn’t black - but also wasn’t white. So they didn’t kill him, right at the outset when he first started hanging around. Major cojones on his part.