Shipping revenue can be enhanced by implementing several invoicing best practices. It is essential to do so, since shipping charges can incorporate a substantial profit. Here are several options:

Prelisted charge. The charge always appears in the default invoice template, so the accounting staff has to take action to turn it off. However, this may mean that the billing person automatically uses the pre-set shipping charge, when the actual amount may be higher.
Full pricing. Include the cost of shipping in the retail price of the goods sold, and tell customers that shipping is free. Though foolproof from an accounting perspective, it makes the prices of the company's products less comparable to those of competitors.
Reminder stamp. The shipping staff stamps shipping documents with a reminder message to charge freight; though this requires the shipping staff to remember to do so.
Billing checklist. Post a checklist in the billing clerk's office that notes every step in the billing process. However, it is easy to ignore this list.
Auditing. Audit a selection of invoices and have follow-up training with those clerks who have forgotten to include the shipping charge.