Currently, many people are selling items in the shop that no one will ever buy, and this is creating so much clutter that it is hard to sort through the shop to find what you're looking for. Someone is trying to sell a piece of string that's named Spiro's toe hair; how stupid is that? Damaged items like stone swords you get from wither skeletons, useless leather armor that is only in there as a gag with some custom name on it. The problem is, these items stay in there until either the owner takes it out or someone buys it, and no one is going to buy it.
What I suggest is if a player is inactive for 1 month, their shop will be deactivated for the time being until they come back, and all items in their shop will be unlisted for that time until said player comes back.