I've completed the trip. The pre-fuel scheme was rather confusing to me on the pick-up.

Picked up the car at Rome Termini station and asked for the pre-paid petrol option on a compact car and was "upgraded" to an Audi A2. To my surprise it was €92! I knew fuel was expensive in Italy, but yikes! The agent explained to me I wouldn't have to pay it if I returned the car with a full tank. I guess because I'm so used to the pre-paid fuel option in the US being that you pay for a (overpriced) full tank in advance you don't get a refund on any unused fuel.

While on the trip I elected to fill the car my self. It was far more fuel efficient than I thought it would be and I paid only €22. I was not charged for any fuel after returning the car.

I was charged for any extra three hours beyond the reserved rental period despite having returned the car 5 hours earlier than indicated on the receipt, but that's for another thread...