Sixt Trustworthiness?
 

Are all the reviews I see like this one normal for Sixt? Also, their online responses seem pretty indifferent.
Example: Bad Choice!! Received no invoice at drop off then was emailed the invoice a day later. Saw the charge was 50% higher than expected and called to complain. Guy said he agreed and would see what he could do. The original charge disappeared off my credit card pending charges and I thought they were adjusting the charge or going to write it off. 2 1/2 months later the original inflated charge comes through on my statement. I call my credit card company who conference calls me with the Sixt rep. He tells me about charges that don't even match the charges on the invoice and then says if I want to talk about an invoice adjustment, I can call him back in the morning and he can give me another number to call for billing customer service. I said I wasn't going to call in the morning, just transfer me or give me the number now. He said no... I would have to call him in the morning. I disconnected from him and told the credit card company to dispute the overcharge. There is no way I am going to let this company scam me out of the money. Do not roll the dice with these people.

In the past 5 years I have rented many times from Sixt in Argentina, Mauritius, Spain, France, Germany, and the UK. Mostly in France and the UK though. I have never experienced anything like this. I would advise to be very careful at the rental desk regarding the agent trying to sell extra insurance etc though. I would say they are sometimes a little too proactive, particularly using the extra insurance as a bargaining tool to give you a really good upgrade. Although I would say a few years ago at Malaga that agreeing to buy extra insurance for 10 euros a day in order to get a "free" upgrade from a BMW 3 series manual to a brand new top of the range BMW 7 series was a bargain, so it is always good to look at the bigger picture.

Apart from that the usual caveats of renting a car from any company apply - always photograph all damage on the car when picking it up to avoid charges.

All in all I find Sixt far better to deal with than the other companies I have tried regularly (Avis, Europcar, Enterprise). I have never rented from Hertz so cannot compare them.

I would say that in France I have had many bad experiences with Avis (fictitious traffic violation charges, horrible dirty high mileage cars, lack of choice of premium vehicles) and Sixt is just totally different and much better from the nice attitude of staff to the big choice of vehicles.