I feel like we've all had this discussion before. Perche is basically correct. Italians in general are pretty straight shooters. That's why Perche can take photos in a Roman restaurant of women's purses left on empty chairs while their owners went out to catch a smoke and not be a witness to theft.
I've personally taken dozens of taxis in Rome without once being scalped. Even during rush hour, the routes taken, while circuitous, were the most efficient (and end up costing me far less than the direct route clogged to a standstill). But can there be rip off artists driving cabs in Rome? Sure. Anyone who's tried to grab a cab in to Walls from CIA knows what that looks like. Also, I have to say if you jump in cab in Naples, if you're not prepared, you will be overcharged. I've gotten quoted fares as high as 35€ for the 11€ fixed rate from Centrale to Beverello. But even there, another driver walked over and offered 20€. And eventually took 11, when I produced the fare card I'd downloaded.
(Btw, unlike Perche, I only speak basic - extremely basic - Italian. This hasn't made me "mark").