The Black Bazaar was decidedly the worst place in all of Sunagakure, which is why when the village moved to the surface this location remained buried within the old ruins. Anything you could want on the black market can be purchased for the right price. Under the guise legitimate business, secrets lie hidden. Human trafficking is a major problem in this area but the ANBU have made strides to reduce the incidence of future atrocities but they cannot be everywhere at once. There are several gangs who run the Black Bazaar as though it were their territory.
The Black Market can be found here. Known for selling illegal shinobi "parts", human livestock, forbidden seals, and other nefarious things.