Gas station credit card skimmers have evolved to be visually undetectable because they are installed on the interior of units.
learn.sparkfun.com/tutorials/gas-pump-skimmers Hide your credit card, hide your wife. There are only three defenses now: scan the area for the presence of wireless signals coming from the unit, only use gas stations that take chip readers, don't use credit cards at gas stations. And as a last ditch effort, make sure you review every purchase every month.