Personally, I find it quite an annoyance to deal with car rental. I always end up singing a two sided paper with small print, simply because I am to tired to bother. That this is naive approach was proven, when I was the receiving party in a rear-end accident. ALthoug it was clear from the start, I wasn't liable rental agency still deemed it appropriate to take 500 Euro from my Credit Card. I heard from other that this common practice and you need to explicitly take insurance against this. Since, this accident I always ask, but in many cases you still remain liable for at least 500 Euro (sometimes even 1200 Euro) in case of an accident. In the end you can get your money back, but I learned from experience that this can take up to two years.
With this in mind and my (naive) desire to sign only if I know the consequences I am wondering if there isn't a car-sharing or rental scheme that works globally with one contract and covers all insurances in a similar manner? Also with a clear picture on the amount you are liable for in case of damage.