I rented a car from them in Frankfurt airport. When returning the car to them they showed me a minor scratch on the windshield (it was there before, but too minor to note), and charged me 800 Euros. I checked on the market, and the repair should cost only 100 Euro. Furthermore, they could not show that they indeed fixed it. As far as I know, they may be charging the next hirer (and the next one) for the same scratch. I suspect that this is what happened to me.