I did a customization of the order confirmation for a client, where a big brightly colored subreport splashes across the page with "Do Not Ship" if it finds an overdue balance or credit limit issue, and lists outstanding invoices.  Then through the wonders of PrintBoss, a copy prints in the collection person's office so that she can contact the customer if appropriate.  Proper credit limit setup should force an approval as Jay and 49153 described, but this solution also helped let the person entering the order understand the issue.

I did a customization of the order confirmation for a client, where a big brightly colored subreport splashes across the page with "Do Not Ship" if it finds an overdue balance or credit limit issue, and lists outstanding invoices.  Then through the wonders of PrintBoss, a copy prints in the collection person's office so that she can contact the customer if appropriate.  Proper credit limit setup should force an approval as Jay and 49153 described, but this solution also helped let the person entering the order understand the issue.