Naples airport to Napoli Centrale

It used to be possible to take a local bus, but I believe that is no longer an option. There is an airport bus every 20 minutes or so, costing €5 - and that would be my choice. I seem to remember that a taxi has to charge fixed rate of around €20, but I am open to correction on that.

Yes, there is an airport bus direct to Napoli Centrale.
It's called the Alibus.
It only makes two stops, and the first is Napoli Centrale; it might say Garibaldi as the station is in Piazza Garibaldi.

http://www.anm.it/index.php?option=com_content&task=view&id=1314&Itemid=373
You'll have to translate this website.

We had to return a rental car at the Naples Airport and then get to Centrale. The taxi we jumped into wanted to charge us 25euro. We said it was too much and would only pay 20. He argued with us, and we grabbed our bags and got out. Another guy came up and said he'd do it for 20. Lesson learned and to be shared: Negotiate and agree to the price before you ride. And keep your eyes closed once on the road. You don't want see the crazy driving...

Anothe approach is to download the city PDF of fixed-price taxi prices and show it to the driver. Circle the luggage-inclusion note before you do. Your Frecciarossa ticket (non-changeable) easily justifies the taxi fare, whether 20 or 25. This is what Rick used to call a worthwhile splurge.

Are you arriving from a Schengen country? Do you only have carry on luggage? If not you’ll be at the mercy of your flight arriving late and a wait for luggage and immigration. Depending on the time you get out of the terminal you should know if you’re able to take the bus or hop a taxi. Make your choic3 at that time but prepare for either option.

"...fixed-price taxi prices and show it to the driver.... This is what Rick used to call a worthwhile splurge."

Not in any way travel advice, just an anecdote, and in no way meant to contradict my namesake's advice.
Our second ever trip to Italy was to Naples, we caught the local bus into the city (no longer an option). We were taking in the views, staring at Vesuvius and discussing the volcano, when an elderly man in front of us turned and said - "I watched the last eruption in 1944 - I was only 10, and it was really frightning"

We spoke for the remainder of the journey, and he told us about the city, where to go and what we might enjoy.

He was the first of many kind and wonderful people we met in Naples over several visits - and something we would have missed had we "Splurged".

TimW

Many thanks for posting this.

We are on our way there soon.