I had a great experience renting a car in Germany that I used in Austria, Germany and France for two weeks. I booked the car thru gemut.com. The car rental service is a family owned business in Oregon. It allows reserving and paying for the car in US dollars vs paying in local currency in Europe. We picked up the car from a mall outside Munich and returned the car to the airport after two weeks. There was no hitch. All went smoothly. There was no up-sale attempts and they accepted my US credit card insurance coverage.
When I rented thru Thrifty a year ago at the Munich airport, I had to go thru the Buchbinder desk at the airport. They charged me additional fees at the time of rental that doubled the costs. Surprise!
the gemut.com website also has great information on car insurance on rentals in Europe.