Perche, my point in commenting on your post was to try to correct the impression that a tourist in Rome could let their guard down more there than they would elsewhere when it comes to taxis.
Whether the Italian cab drivers in general have a particularly prominent criminal sector, is a thorny topic I don't want to wade into! But I do remember reading that Rome's airport transfers' fixed rate was implemented by the government about 10 years ago to combat the many complaints submitted about the drivers and to make Rome more tourist friendly.
I can only speak from my own experience and from talking to my Italian friends in Rome, and based on that I encourage my friends traveling to Rome to use the same "streetwise" sense they do when traveling in other large cities - nicely summed up by you above:
Originally Posted by
Perche
...I think if you get into a cab, you can say in english, "how much will it cost to go to the Colosseum?" Beforehand, you can ask at your hotel how much it should cost, and be armed with that information when you get into the cab. At the airport, when you get into a cab, just ask how much. If they don't say 48 euros, call the attendant that is there. A little bit of awareness can go a long way....