For example, I rented twice this year - I don't own a car and usually use the train - and the first time they wanted my to enter the PIN for the credit card, which I didn't know. A big hassle, they took (real!) money off of my EC card (which I got back afterwards).
The second time I didn't need a PIN (different car rental company), but they helped themselves to almost 800 Euros in alleged damages from my credit card (good thing I had used an online service and opted into the "we pay the deductible", which was 1,000 Euros, on the full insurance I had also selected to get).
