In my modern fantasy novel, there is a species of people called the Hammerts. The Hammerts are small orange humanoids who have issues running and jumping after they reach adulthood. To compensate for their limited mobility, Hammerts all have a supernatural ability to access a hyperspace dimension purely for storing items. Here are the rules of the Hammerts' dimensional storage:

 - Each Hammert has access to their own private region within hyperspace.
 - Nobody else can access a specific Hammert's hyperspace without consent of the owner
 - Items are stored in hyperspace by a Hammert touching an item they want to store for 2 seconds and saying "Banish!"
 - Items are released from hyperspace by a Hammert gesturing in a location for 2 seconds and saying "Summon!"
 - Living animals and sapients cannot be stored in hyperspace
 - No item that weighs more than 10 metric tons or with a volume greater than 20 cubic meters can be stored.
 - There is an unlimited amount of hyperspace available to each Hammert.
 - Hyperspace is a dimension without time, so nothing ever perishes or ages inside of hyperspace
 - Large items can be spawned up to 3 meters away from a Hammert.
 - After a Hammert dies, all of their possessions go to whoever they named in their will. If the Hammert didn't leave a will, instead all of their possessions will be placed in a public hyperspace region that any Hammert can access.
- Hammerts can quickly and mentally filter and organize whatever items they want or need within their hyperspace region.
- Hammerts are the only ones who store items in hyperspace. Another species uses hyperspace for travel, but they can't access private Hammert possessions this way (but they can reach the public hyperspace regions).

A huge issue I realized with making Hammerts is that they would be the world's best thieves. They can just touch anything they want, say banish, and as long as there were no witnesses, they won't get caught. Hammerts could shoplift with impunity. And the best part is that once an object is within hyperspace, it won't come out unless the Hammert dies or the Hammert wants it out. Hammerts would also be world-class drug suppliers and weapon smugglers, but that is another topic.


Without making a massive change to the rules of hyperspace storage, is there anyway to make sure that Hammerts can't or won't take everything that isn't nailed down as long as they aren't being watched? A society with endless theft would be very unstable. Well either that or Hammert nations would have to go full Big Brother with cameras everywhere.