The salesman listing based on invoice date could be used for a commissions accrual entry and the salesman listing based on paid date could be used to set up the payable to the sales person.

From a practical point of view, it would be great if there was an indicator on each line of the customer's order, check box (yes/no), to indicate whether the item is subject to the provision calculation.  It could default to yes and the order entry person could uncheck it.  There could also be a default indicator in the items table which carries over to the line in the customer's order.

This idea came from the fact that certain items billed to the customer (like expense reimbursements that aren't marked up to the customer and therefore no profit, possibly freight, possibly sales tax in the U.S.) do not generate commission to the sales person.