The way it always worked when I have hired a car is that you get a full tank included in the hire price. You either return it full or you let them fill it up for you. If they fill it up they must use liquid gold because thats the price they charge you. When I return it to the guys at the parking lot (who are always more sensible than the girls in the office) I make sure they look round the car with me and check the fuel and note on the paper that it is full. I have never been charged for extra fuel.
I have never taken extra cover and have driven all over Europe. I live in Denmark so driving on the wrong side of the road is natural to me. If you take the extra cover and you are in a scrape, you dont have to pay anything. If you dont take the extra insurance there is an excess of €600, I believe, depending on the damage. As I say, I have never had to use it.
I have never had any problems with rental cars. The girls on the desk must work on commission for the extra insurance and can be pushy. I did once have to say " Which part of no Thank you are you having problems with". But usually it is fine. I always write down all my details before I get to the desk including mobile number, accomodation address and telephone number. They always need it and it saves trying to explain. I think it also gives them the idea that you know the procedure pretty well.
Steve