When you make a booking, the car you hired have an excess, this excess is the value you are responsible for the car in case of accident. You leave a security deposit in the beggining of the rental, and when you return the car the security deposit it's canceld with you. For that you must have an credit card. The credit card must be in the driver's name.
Excess by Groups:
A,A1,C,G - 900€
In each case you can reduce the amount of the security deposit, by making an insurance like this (SCDW or SSCDW), but you allways must have an credit card to present when you pick up the car