I have one warehouse and two sales representatives. Everyday in the morning they come to the warehouse and load certain items in their cars. They go to particular shops each day and try to sell them these items. At the end of the day, they come back to the warehouse to return the remaining items that are not sold. What is the correct way to implement this in Odoo? 

What I am doing is creating an internal location for each sales representative which represent the items in each sales representative car. However, the problem is that I can't select the internal location in sales order.