Forcing Customer Order Entry Requirements

To the list,

Does anyone have specific requirements that the customer is "demanding" and
how do you enforce them?  For example, we have customers that require that
the order be entered with their Customer Item number.  I know that the panel
to enter these items is configured at the user level (not at the customer
level where it should also be required), but the system still lets you enter
in your item numbers instead of forcing the user to enter only the customer
item number cross reference.

 

Besides trying to get the Customer Service Rep (Order Entry Clerk) to do
their job, has anyone come up with a way to handle this with a user exit?  

 

Eric