When you make a booking, the car you rented has a franchise, this franchise 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 is canceled 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 always must have an credit card to present when you pick up the car.