Bukkit

You should make a way so that you can let others access the chest of your shop by looking at the sign you want to add the player too.
Command maybe could be /shop trust

This is still difficult to do as ChestShop does not store any additional information besides the one on the sign about a shop. It would actually be easier to give access to all shops instead of an individual basis.

Actually it might be already possible to do when disabling ChestShops build-in chest protection and using LWC to autoprotect shops. Then you can manage who has access to the shop's inventory via LWC like usual.