Most games update the Stores either from Region to region, so the last town has the best items, and some update the Stores with the progression of the story. Dark Souls 2 had a concept i never saw in this exact way. When you spend a significant amount of money at the Shop, they merchants feature new stuff, which can happen up to 3 times, their attitude changes, from being poor and humble to being rich pricks and you can get special gifts. You get a rar ring when you spend 10000 at one Merchant while the other one gifts you a set of armor when you talk to him with no money in your pockets. Could you add something like this? Not total Shopkeeper progression, but acknowledgement of the player buying stuff. Maybe the Hatter can afford an apprentice when you buy enough, who is present in the Shop later. Maybe the Smith(or his daughters) gives the player a quest for a fabled weapon, if you own all the suff they sell at least once. Of course it adds the problem that some players won't find those events. I mean, who remembers to talk to all of them every time.