Bartender Scam

Whenever I'm sitting in an airport bar, killing time between connections, it seems like the bartender will put a check in front me and say, "This isn't your check, I just have to put one here." I asked my old bartender friend about the practice. He said that the bartender is probably ringing up fake orders for lower amounts and then pocketing the extra money when people pay with cash. A bold move to be sure, but I feel like it's acceptable compensation for having to go through airport security just to get to work each day.