Heads up - the fixed price fares have been rescinded in Naples two weeks ago. All on the meter now or negotiated directly with the driver.
For now the City has suspended the fixed price fares only until May 11, 2023.
This was in response to the protests by the taxi drivers who said that due to the numerous road work sites opened by the City in the streets of Naples, they are unable to reach the customers' destinations in a predictable timeframe.
Do not negotiate with drivers!
I agree with Dario. Last time I negotiated the price with a taxi driver in Naples (many years ago) I discovered that the taxi driver gave me a “deal” that was much more than the price I would have paid if I paid by the meter. When bargaining with a Neapolitan you will always be on the losing end.