If some knucklehead got caught with a few cards he lifted from someone's wallet and got caught using it he would be handled by local cops and it would be a slap the wrist and some restitution. If the local cops were told the cards were bought from a guy who worked at a post office, the postal inspectors would get involved. If the cards were counterfeit, the secret service would get the call. If it was identity fraud, the fbi and postal inspectors would be on the case.