How
People turned up with with a new Chip-n-pin card unit (they were just being introduced) and told the part-timer behind the desk that they had to be changed. The new unit read all the details from the chip (which is enough to reproduce the mag-stripe, together with the PIN that was typed in. The units that I am aware of then sent batches of numbers by SMS to a mobile registered somewhere in the East, so impossible to trace.
Bogus cards could be made for cash machine use, and together with the snaffled pin gave free money...