I am currently writing a seminar paper on the perception of the second-hand trade in the early modern period, in literary sources of the time.
While working on my paper, I have however become intrigued by the question If and how flea markets (and other avenues of second-hand trade) were portrayed in paintings.
Were they portrayed as dirty and places for the poor, or for fine people interested in antiquarian culture?
Would the vendors be depicted as upright businesspeople or as untrustworthy?
And would something as mundane as a flea market find itself into artworks of the time at all?
I'll give my usual caveat that I'm not a qualified responder, and certainly not the best person to answer this question, but I wanted to know if you've checked out the genre sketches and prints that were popular in the late 17th to early 19th century of street people in various cities?
If they were published, they often are published, either bound or loose, under the name "Cries of London" or the city they depict. Here's links to a few that are digitized:
The new cries of London by James Bishop, 1844
London Cries: A Man with a Bundle, Old Clothes, Paul Sandy, c. 1750
There's also an excellent collection of sketches published in book form:
The cries of Dublin & c : drawn from the life by Hugh Douglas Hamilton, 1760
For analysis, it's worth noting that the second hand is depicted as a trade for the lower classes that serves the lower classes. Note how all of the sellers are depicted in worn clothing themselves.
I'd also suggest reading Elizabeth C. Sanderson's article in the journal Costume.
I'm sure someone better versed in the art history of the period can give you a more academic answer, but I hope this helps.