@JaneCavanaugh correct, ""Allow Back Orders"" option at the item level, or default from product line, determines if a short shipment generates a back ordered Sales Order line. This however does not guarantee that the order qty = shipped qty, since you could ship more or less than ordered. If they are using Shipping Data Entry, you can prevent the over shipment using the Shipping setup option, and uncheck 'allow overshipment'. If your customer needs exact order qty = ship qty I'd put in a script to handle it.