Here in Philly there's always a scammer who will approach you after you swipe your card and tell you that the pump you're trying to use is out of order. As soon as you move to the next pump, they're pumping gas on your credit card. Another scam I've seen is where someone will approach you, offer to pump your gas, and wait until you drive off and pump more gas for themselves. I can't go to a gas station in the city anymore without someone trying one of these two scams on me.
I don't know if all gas stations do this, but the ones around here limit debit card transactions to $50. Anything over that and you have to swipe your card a second time. I guess they do this to prevent someone from pumping hundredes of dollars worth of gas after you pull away without closing the sale.
BTW: Sorry, I just noticed I was in the JBT forum. I'm not a cop, but the info should still be relevant.