Ultimately the real reason why Wandering Shops wander.
The wandering shop run by the consortium of Skillet, Wang, Yrxle!yt, Bunglestiff, Cwmlad and Patel has one of those jolly little advertising notices on the door advertising its status as Open or Closed. The obverse face carries the legend Closed - even for the sale of Necromancer cigarettes.
This worked as a jocular way of indicating to disappointed customers that the store was closed for business, without giving undue offence. Right up until the moment that a real Necromancer turned up, a second or two after closing time, to negotiate the purchase of a packet of cigarettes.
It is rightly said throughout the multiverse that you should not interfere in the business of Wizards, for they are subtle and quick to anger. This especially applies if they are out of smokes, suffering from nicotine withdrawal, and in a position where not only is some little jobsworth in a green apron refusing to open his miserable little shop to me, he is also snickering into his hand at my discomfort.
An angry wizard, contrary to popular opinion, is never subtle. Not when he really, really, needs a cigarette. This wizard cursed the shop and decreed that contrary to the sign on the door, it would never again close and shall be open for all eternity. The multiverse obligingly rearranged itself to make this possible. And thus we have Wandering Shops, or at least one...