White Dragon wrote:
"She thought it was an actual, physical place - a street market in a shady alley some where."
In her defense, the "black market" describes both the concept of a way to sell wares illegally and the places that pop up on occasion to do that.
"I knew someone who thought the same thing about black markets! She said she always wondered why the police didn't just go there and arrest everyone!"
These days that sort of thing is almost always handled online but back before widespread Internet the black market was often a place. It was just usually either well hidden or kept moving, and police often did do exactly that when they could find such a meetup.