In 15 years of visiting it has always been the taxis of Rome that I have found dishonest. Once I was shown the date as the fare, another time the switch from a 20 euro note to a 5 euro note. A slight of hand by the driver. A premium charged for entering the Vatican City, not even in the city yet. Refusal to use the meter so it was fixed price. Told that this is very far away and wanted 50 euro, when turned away I got a cab for 15 euro. Interestingly when the cab driver talks about being aware of thieves, I am most on guard. Another time thrown out of the cab because the driver spotted an airport fare (people with luggage). I could go on and I would say this relates to maybe less than 10 percent of cabs, but they are out there. An Uber like system would stop all of these abuses.