The Shop is a major module which can be researched at relics. Upon installing a shop, any discovered merchant on the floor will be teleported to it. If a store is occupied by a merchant and is being operated, it will generate an income of Dust-per-door (you will see a positive number added in the turn-based resources in the top of the screen in the Dust meter). Note that the merchant still sells the same items as when discovered and its items prices remain paid with same resources.
A Shop occupied by a Merchant gives 1 dust for every 10 wit used to operate it. This amount is rounded up, so 1-10 wit gives 1 dust, 11-20 wit gives 2 dust, and so on. Having a Shop operated by a hero (possibly augmented by Mechanical Pals to increase wit above the next multiple of 10) can yield a significant income of dust. A single unaided Mechanical Pal will yield 1 dust if built in a room with an occupied shop, making it useful to have at least rank 1 Mechanical Pal unlocked throughout the game.
It is possible to generate 10 dust on a floor, but it is extremely rare. A player would need to find 2 merchants and 2 rooms with 7 minor module spots and a major module spot. Placing down 7 Mechanical Pals IV would produce 2 Dust per room, for a total of 4. Then two operators with 23 wit would bring 5 dust per room, for a total of 10 dust ever door. This setup allows one to power rooms as soon as they enter.