I was in Italy in the summer, and on a gas station happened the following:

It was a "self-service" gas station, without staff. Before I refuel my car, it was needed to insert my card (payment possibility was only with card), and the card reader automatically subtracted 100 Euro as "guarantee". After I refuel and piad the gasoline, the amount of 100 Euro was redistribued to my card instantly...

I think this is the "digital version" of shopping cart theory :)

And be careful when you refuel your car in Italy...you need to have at least 100 Euro more, than the value of gasoline :)