It is possible to propose the facility on the customer order header (OIS100) at CO entry. The proposal can come from the customer, the user, the division, or the order type. This functionality is enabled using the field selection on the order type in 'CO Type. Update Field Selection' (OIS014/E).
If an M3 user is not restricted to enter customer orders for one facility, the user will need to enter the correct facility when creating a customer order. As the user might not know which facility to use, looking up details on the customer record (CRS610/G) when creating a customer order can be a problem (especially at call centers).
Customer orders created via batch order entry might be another problem. In order to control the facility per customer, a customer specific record need to exist in 'Settings. Batch Orders' (OIS278).