does car rental insurance in europe (full cover) always has a possible certain amount of money that the renter may have to pay in cawe of accident/theft?
Yes, there is always a deductible unless you buy the "super" insurance (additional cost) that also covers the deductible amount.
...and somtimes they will put a "hold" on your credit card for that deductable if you don't buy that "supplemental insurance". Ask the rental agency before you rent!.
On our X Mass trip to Portugal I used an agency that I don't normally use, and they hit my C card up for $2500. That was not a problem for me, but for some people that could be.
Sometimes your CC will cover that deductible (but some rental agencies will not honor that!); also check with your auto insurance company.
And lastly, minimize this problem by renting your car thru autoeurope.com. My TA and RS talked about them. They are a broker that handles all of the majors; Hertz, Avis, Europcar, etc. Their rates are fantasic. Go to their website and fiddle with the cars and coverage. If you have ANY problems with this call them up. They are super helpful, and will guide you thru this.