Potomac Attire is one of the shops located in the Market of Rivet City. Run by Bannon, Potomac Attire sells armor and clothing, and usually has around 300 caps to barter with.
But he don't have much of that armor does he? Sure if I was living in rivet city I might buy some clothes from him time to time, but I don't.
I think they only had him there to keep it "real", but even so He probably doesn't turn in much profit.