"Gas station credit card skimmers are external devices that thieves attach over a real credit card slot at a gas station pump. As customers swipe their cards into the skimmer, the device saves and stores card information immediately.
"What to look for: If a credit card slot looks different from the other card readers at the station, it might be a setup for a credit card skimming fraud.
"What to do: Skimming devices are meant to be placed temporarily for a matter of hours or just a day. For that reason, they are attached using only double-sided tape, so thieves can easily remove them. Before sliding a credit card through the machine, tug on the reader to ensure it is securely attached; skimmers will easily pop off with little effort."
Read the rest of these fairly clearly presented tricks at the gas pump - and possible ways to outwit the scammers, scanners and skimmers :