How about adding another feature to shops: a limited stock. This might allow for other items, like healing potions to be sold again (like golden potions finally available to paladins too ), without risk of people buying silly quantities. Best would be a gradual increase of stock (until a maximum is reached), to mostly prevent people buying as soon as it's in stock again.
Also, what may be interesting, is special items, for sale only once (and of course only one available). Especially without any warning message, might get interesting who finds that item first . But of course, this would be non-automated, so might be a bit labour intensive, though it shouldn't happen often anyway.