Halazar's Fine Gems
This shop has a glistening black front kept shiny with magic. In its center gleams a single sparkling (and illusory) gem the size of a man's head. Those who touch the gem feel a wrenching shock as the magic drains a small amount of their energy to sustain itself.
The establishment prides itself as much on its expensive prices as its magically shining black walls, as it houses the finest gems one can find for sale, exquisitely cut and mounted, displayed in severely simple glass cases, and sold for roughly four times what they'd fetch elsewhere. Waterdeep being what it is, the gems do sell, and folk proudly boast of how much they paid. The security arrangements are confidential, but powerful.