ToME WikiThis is pretty simple; each shop should be guaranteed to have certain items always in stock. For example, the General Store would always have rations, light sources, unenchanted cloaks, spikes, and diggers. The spellbook shop would have the first spell in each realm (and the Beginner's Cantrips book). Alchemists would always carry identify, light, satisfy hunger, word of recall, and maybe the stat-restore potions. And so on. I'm envisioning these as being inexhaustible supplies, which has the side-effect that stores would never be able to be bought out.
The main goal is to eliminate townscumming for items that the player depends on to play the game. There are certain items that most players would be considered insane to go without (e.g. food, teleportation); those items should therefore always be available.