An interesting alternative concept on how to handle "call shops" would be to continue to have regular shops (which Deckiller does), but use the call shop scrolls to sell items at a cheaper price than in stores. Furthermore, the higher the level of the shop, the better items it sells at a even lower price than the merchants back in town. It would make finding the scrolls a lot more exciting but also a lot less common.

This was sort of put together when I just woke up; I apologize ahead of time if it's a little dumb.