Purchase order items are returned but still appear on the appointment with costs affecting margin. How to prevent this?

I’ve created a GI to find gross margin on appointments. One issue I’ve run into is that if a purchase order has been returned, the item is still on the appointment with the costs showing but it is marked as “completed” as well as a “free item” to remove the price so it doesn’t bill out. Is this an issue with the steps purchasers are taking, and they should be doing something differently on the appointment? Having theses costs show without a price is greatly affecting margins on some appointments.