When a customer required on sales orders

There is a system reference to set customer to be required on sales orders. If the system reference type 'SALES', system reference 'CUSTOMER-IS-REQUIRED' has a value of false, then a customer is not automatically required for every sales order. See Sales system type

The exception to the rule is as follows. If a sale order has a back order, you must always enter a customer. As the system has to know the customer for the back order. We can't change this exception. As back order tracking requires a customer.

If you want to process sales orders for cash customers with back orders. Create a customer card called 'CASH', set the card to be on stop, so no account sales can be made on that account.