Sixt, specifically their Aachen location, will bill you at a higher rate than what you agree to in…read moreyour contract, and you will have to really fight them to get your money back.
I signed a contract for 314€ and was charged 456€. There was a (correct) excess mileage fee of 17€ as well as a 12€ incorrect late return fee. I took a picture of the keys as I was turning the car in on time, and good thing I did because they required proof in order to take off this incorrect charge.
The rest of the ~110€ difference was from an increase in the day rate for the car above that which was listed on the contract I signed. They gave excuses such as our car being upgraded. We were not upgraded, and it was not in our contract. I called, emailed, showed the contract, and was eventually told that "As you signed the binding contract, we must respectfully decline your request for a refund". I kept calling and was eventually apologized to and given a refund of the overcharge. It took days and a lot of work.
Based on the number of people I talked to who refused to see a problem, their business model seems to be: require a down payment; overcharge travelers; and count on a percentage of them to give up on recovering their money. If we had not elected to purchase complete insurance coverage I am confident they would have trumped up a bill for nonexistent damages as well.
The car itself was great, and the front desk people made sure to give us big smiles the whole time.