From the customer’s standpoint, the checkout process is just a small part of a transaction. Granted, it’s the part where he pays for what he bought, but that’s just a minor inconvenience. Much more important—and certainly more fun—is the part where the customer receives the item(s) he purchased.
Which brings us right to the process of shipping those orders you receive. PayPal is intimately involved with several parts of the shipping process, starting right up front—where you decide how much you’re going to charge the customer for shipping.