In videogame dungeons, in the midst of Everything Trying to Kill You, one may find shops selling all sorts of items, varying from not actually useful to somewhat useful to absolutely necessary. If the shopkeepers are standard NPC types, there is the Fridge Logic question of how they made their way down there in the first place without getting slaughtered, and what shortcuts they are using to bring supplies in (as they often will restock after a while). The shopkeepers need not be Muggles, though; they might be friendly versions of the local monsters. See Intrepid Merchant.