This is the shop room encountered within dungeons. Three equipment or food items are randomly chosen and can be purchased at a hefty price. Bear in mind items generated can result with equipment you are already equipping. Sometimes there are chests or barrels at the edge of the room for extra enemies, treasure, cash or items.
If you don't want to pay the prices shown, you can attempt to kill the Merchant - once you begin combat items will become free, and doors will close until player or Merchant is dead. If you kill the Merchant then Merchants in subsequent shops on your run-through will attack you upon entering their shops.