Shops in Elysian Tail work differently than one might expect. Upon running into your first shop in The Glade, the shop keeper there tells you that if you bring him any new material, he and every other shop in the game will stock a certain quantity of it. This makes many a fetch quest requiring a ton of a specific loot drop infinitely easier, assuming you have a minimum of one of the loot and a good bit of patience to wait while the shops restore their wares.
While it may seem tedious, stopping by a shop every time you run by it and selling one of something the shop doesn't have is a very good idea. Not only does it give you a little money, it also ensures that the loot you just sold is now stocked by all of the shops in the whole game. This affects how fast quests get done as well as how easy it is to get materials for the blacksmith.