Help me!!!! transfer Items when location not enough.

Dear all,
Thanks for reading this topic. I have 3 locations, I set 3 users manage 3 stock. But salesman at this location can sell products from others location (They click at "Deliver from Location:" and change Location and sell) I can not control. I thought over about that and had 2 ways.
1. I lock drop list of Deliver from Location. And they can not sales at another location.
2.    There are 2 cases:
        + If they have permission, (they can transfer Items) a "Inventory Item Status" windows appear. They can transfer Items if they want. It will be recorded at history.
        + If they don't have permission,  a "Inventory Item Status" windows appear. a notice displays and said contact with administrator.
Can you help me to resolve it?