We rented Nissan Qashqai at Brussels airport in Feb 2014 for one day. The price was very attractive and the car they provided was Nissan Qasqai with only 2000km on it.
On return the agent immediately spotted minor almost invisible scratches on the front bumper (seemed like he knew what to look for and where) and blamed us. In June they sent me a bill for 795 Euro for fake repairs.
SIXT IS A SCAM COMPANY. DO NOT RENT ANY CAR FROM THEM UNDER NO CIRCUMSTANCES.
Their business model is charge money for fraudulent damages

I rented a car on Geneva Airport. Now SIXT is claiming that front bumper is loose. I am absolutely sure that I didn't have any damage. Glad to hear that it's just the way company tries to make extra money. I will not pay. It will be interesting to see how far they will go.