Ah, great question. It's covered in depth in our book. Nutshell: they have a group of accomplices on standby. They call them "look-alikes." When the pickpocket gets a credit card and ID, he calls up the accomplice who looks most like the victim. The accomplice practices the victim's signature a time or two, then goes to collect the cash advance (which the thief applied for at a machine.) The harried teller or cashier takes a quick glance, sees a vague resemblance, and doles out the cash under pressure to serve the next person in line. On behalf of police, we have interrogated those who commit this particular M.O. Interesting, eh?