You say there were a bunch of empty taxis, with no drivers sitting in the cabs, hoping to take Pitti Fashion show participants home, off meter, for a higher price.
Not so. Everything points to Florence bringing in 100 extra taxis to deal with 3 major events at the same time, and those taxis weren't empty because the drivers were looking to take people "off of the books."
Florence brought in 100 extra taxis for all of the events, and the drivers, virtually all of who live in the outskirts, were so gridlocked in mass summer tourism traffic that they couldn't get into the city to drive them.
The continued bashing of taxi drivers, most of whom are very professional, seems way out of line, especially when Florence doesn't have Uber because it is estimated that there are only about 30 people in Florence who are currently driving there with a valid license, a state inspected car, and who have passed a criminal background check.