Default site - newbie question

[DBergkamp10]

We have sales reps across the country, and they each have their own Site ID for inventory. When they are entering orders from the Business portal, it is my understanding that any orders they enter will use the default Site ID for our head office. Is there any way to get these orders to take the stock items out of the inventory for their own warehouse? Otherwise we are faced with a situation that their orders will have to be changed line by line at head office before/during invoicings.

Thanks in advance

Ivan