We rented a car with dollar - we ask them not to add any insurance on the contract. They did not.
A week later we had to exchange the car because of weird noises coming from the car. They exchanged it quite easy, but added an insurance for the new and! for the old contract - without letting sign us anything, they added an additional insurance for already past time! They just took the money from my Visa Card without asking for it.
The second car was kind of broken too, but we didn't drive too much for that we would have needed to exchange it again. I can't recommend to rent with Dollar! It was 120 USD more than expected without ANY REASON and with more trouble ever!