We made our first trip to Italy last winter. We got a credit card that did not charge an extra fee for using overseas. Before leaving we contacted the credit card. They said we had to refuse the insurance (except the mandatory fee) or they would not cover anything. We did receive a letter to give to the rental company. We showed it to them - though since they didn't speak much English, I think they took our word for it. We did not have to use the insurance so have no first hand experience.
One other thing to watch for, as you are driving along there will be either overhead (on the highways) or orange posts that have the speed limit marked on them. They check your speed as you pass by and a ticket will eventually make it to you via the rental company. If you do a search for access italy/driving in Italy part 10, you will find a handy guide to what the traffic signs mean. While signs to let you know how far it is to the next town are almost non existant. Speed limit, ...not allowed, return to previous speed limit, etc are everywhere.
So far, 6mos later, we have not received any tickets! Here's hoping it remains that way.