This is an epidemic at gas stations in Southern California. I've been nailed by skimmers in LA, and a lot of my friends have too. My girlfriend refuses to use the debit cart option at Arco gas stations for fear of her card info being stolen again, and its a legit concern.
They're impossible to spot unless you plan on trying to pry off the front of every payment kiosk, which as far as I know most banks and gas stations frown upon...