Add to the rule that you can't FORCE people to give you storage access, as it does not make sense to put items that you've just mugged off someone in to their storage chest.
But if this is the case then I think you should also make it unrealistic to give storage to random people? Because it's unrealistic to give them access to all of your items, because if we're talking about realistically; they would be putting it in the exact same chest as you i.e the chest would be shared between all people there accessing it meaning all items would be accessed by everyone.