Well, I'm not sure about fedex but at ups every end of the month they get a bill for everything they have sent. Someone could figure out someones account number easily and send a ton of packages, and get away with it. Only thing that could go wrong is if the account owner contacts the company before and they mention it.
I'm talking about those print-at-home shipping labels that most shipping companies offer. I'm wondering what would happen if someone did a charge back on their credit card after the package was already in transit.
Would the package be rerouted and returned or is it home free after the barcode is scanned at the first post office?