Credit Card at Air Machines
Avoid using the Credit Card at the Air Machines
If you need air in your tires the new air machines are great. These new machines make it easy to know when your tire is properly inflated. When the tire pressure is right - you'll get a couple of audible beeps.
Credit Card Options
Some of these machines now include the option to swipe your card to pay and enable service.
The problem is that if the machine isn't working there's no way to know if the charge went through. I have seen these new machines out of service at different stations.
If you swipe the card multiple times you may get charged for each swipe.
For security purposes, I would recommend just having the proper change in the car. Having $2 in quarters in your glove box would be a good idea. That way you have enough change in case you ever need it.