With most e-commerce solutions some or other item is ordered at the end of the checkout process. In many cases these items also have to be shipped to clients. We have successfully integrated with Fedex and Dawn Wing in the past. We have been extensively involved in the processes behind the scenes that can become very complex. Integrating with a shipping company requires advanced workflow management on the sellers side. If you loose track of a parcel or can't match up an order, you are going to have many unhappy clients.