I use rental cars all the time and Sixt are my 'go to' company for leisure and I've rented from them throughout Europe. They're not allowed through my organisation, however which is a shame.

I have encountered numerous problems. For example a car that was filthy inside (crisp packets on the floor, etc). Cars frequently do not have all of the damage marked on them when you collect them. That said, the customer service on fixing these issues when raised is excellent and where appropriate compensation is made without prompting. I regularly get free upgrades and I find the staff at my local branch friendly and helpful.

Yes these problems shouldn't occur in the first place but I judge a company with how they deal with problems. I have experienced problems with other rental firms where they may basically flip you the finger unless you're a corporate client.

I've got a Sixt car at present. It was brand new with 2 miles on the clock when I collected it last week. Let's hope there's no problem in returning it tomorrow...