I have read that there can be problems with taxis in Rome. How can you choose the reputable taxi companies?
According to RS,"only use official taxis, with a"taxi" sign and phone number marked on the door. By law, they must display a multilingual official price chart". Hustlers and rip-off artists used unmarked "EXPRESS" taxis at airport and train station. RS Italy guidebook also gives estimates what typical cost will be from here to there.
And at least in Rome, you can't "hail" a taxi. You have to go wait at a Taxi stop sign until one comes by. Or call a phone number to request one.
Don't take a cab from anyone who offers you a ride. Just go to a cab stand and take the next one in line. They should have SPQR on the door. Before you get in ask what the fare will be. They should be able to give you a very good estimate. You probably won't use cabs to get around the city. You might use one to get to and from the airport but for everyday site seeing you'll either walk or take a bus or the metro. Donna