API address verification during registration. Many customers dont enter their addresses correctly (street ext., zip codes) and we need to know if they are residential or commercial. If this info is incorrect once u ship, UPS/FedEx will fine u up to 10.00 per address per incident. There are several products out there already offering this. Experian is one. A great add-on.
Robert Lieberman commented
Would also be good because we have had cases were customers type in the zip wrong and the FedEx module won't display a shipping price (because the api returns a zip/state mismatch error) and our customers don't understand why they dont see shipping costs.
Bret Calhoon commented
if you have an account with fedex for example you can use their address verification method via api. you may need to have xcart help you tie it in, which I doubt will cost much. but its better than waiting for a fix.