Yes, car rental agencies in Germany are pretty meticulous when inspecting return rental cars.

First, if you are relying on coverage through your credit card, make sure it covers international rentals. I've seen cards that only provide coverage on domestic rentals. The AMEX premium policy seems like a good deal. You may also want to check with your own car insurance provider - they might be able to provide rental coverage as a low cost add on to your existing policy.

Second, as AlienInTheFatherland said, you should be meticulous in inspecting the car and noting damage with the company when you pick up the car.

Third, don't stress over potentially cause damage. Germany is a safe and easy place to drive. With 4 or 5 rentals and a European delivey covering a couple thousand miles, we've never had any damage to a car.

And finally, do the return walk around with the rental car agency employee doing the inspection. While they are fair and honest in my experience, you should double check. Remember any claim for damage to the car can be disputed.