This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
The Mercantile was a marketplace in Requiem, Hima, in the 32nd century. Located inside a hovering building and connected to the settlement by a walkway, the Mercantile was a holo-trading center jointly operated by the Orions and the Andorians of the Emerald Chain. The Mercantile was guarded by regulators and employed an army of drones for various tasks around the marketplace. Regulators were allowed to have weapons in the Mercantile.
The most restricted area of the Mercantile was the vault. An attempt into the vault by an unauthorized individual would result in them being trapped in a stasis beam, placed under arrest, and being interrogated by the regulators. One of the probable fates for individuals stealing from the vault was death.
At the Mercantile, each trade was identified as an order and given a identifier number, such as "Order 7543". During a trade, a holoseller would fix the price for an item and a holobuyer would negotiate the price. If both parties agreed to the price, a deal was struck. After signing off on the deal, a regulator would confirm that payment had taken place to the Orions. In turn, the Orions paid couriers, like Cleveland Booker and Cosmo Traitt, in dilithium to pick up and deliver the items. The couriers were permitted to make their own deals, such as Booker's failed attempt with Hadley to trade Michael Burnham's tricorder for dilithium.
In 3188, Michael Burnham, escorted by Cleveland Booker, visited the Mercantile with the hope of contacting the USS Discovery. As for Booker, he was there to trade in an item for dilithium, which was needed to power his ship's quantum slipstream drive, so he could complete his run. (DIS: "That Hope Is You, Part 1")