The Black Market is the Rogue Isles equivalent to the Wentwork's Fine Consignment franchise in Paragon City. In fact, some speculate that Wentworth's actually created the Black Market there as a way to expand into that area free and clear of the U.S. embargo. (Note: CEO Andrew Wentworth strongly denies any such allegation.)
The Black Market is a part of the Rogue Isles Infrastructure; the essential group that keeps the Isles going in spite of who is in charge.
(See also: Rogue Isles Infrastructure.)