I did reserve online via Travelocity a rental car at the Dusseldorf airport. The best deal was with Dollar rent a car so I did proceed with the online reservation and selected not to have the CDW or LDW as I am already covered with my American Express platinum card. (to note this is not the first time I do rent a car using my American Express coverage) During the whole process of the online reservation there was no mention of Dollar requiring to buy their own insurance.
When yesterday I got to the Dusseldorf airport to pick up my car (at the Hertz counter as Dollar doesn't have its own) the employee immediately asked if I was aware that I had to purchase Dollar insurance and that Dollar does not accept any other insurance coverage. Apparently the Herz employee mentioned that this is an issue they have every day with people renting Dollar or Thrifty cars.
I told him that no I was not aware of that and when I did the reservation I did specify that I didn't want the insurance offered by Dollar and the reservation went through without any issues. I told him as well that American Express platinum offers coverage and that I wouldn't be uninsured. He said that he could not give me the car if I would not accept Dollar coverage (effectively doubling my rental fees). I called travelocity that tried to talk with Dollar but without any success.
At the end travelocity was able to find me another deal with Alamo but once you are in the airport it is very difficult to find good rental deals at the last minute and that is what made the Dollar process unacceptable and a real scam because they count on you having no choice once you show up there and have no other alternative than to accept their offer.
Dollar is entitled to refuse coverage they do not like BUT they should do that when you make the reservation and not 3 weeks later when you show up at the airport. They obviously count on misleadiung people by attracting them to interesting deals only to change them at the last minute.