[ Register or Signin to view external links. ]

The earliest and easiest opportunity to obtain it is in the very beginning of Mission 2, Edge of the World.

At the start of the aforementioned mission, you will be dropped off at the docks of Karnaca with an objective waypoint on your HUD that leads to the Black Market in town. Follow this objective marker through the apartment, but when you reach the second floor, rather than continuing on towards the shop, jump out the open window and into the alley where Mindy Blanchard is located. Take a right in this alley, open the locked gate, and move forward until you reach a patio with a few civilians. The building on the left-hand side of the patio has an open window with a dead body hanging out of it.

Climb into this building and make your way to the topmost floor. You will eventually reach a room infested with bloodflies and a nest keeper. Eliminate the crazed man, destroy the glass display case in his bedroom, and loot the key within. Now return to the alley where you found Mindy Blanchard; there is a door alongside the building here that can be opened with the key you retrieved. This is the backdoor to the Black Market shop. Cross through the threshold and you are now free to loot as much as you want in the shop. The achievement will unlock after looting any one item.