When my wife and I were on our Honneymoon in Europe, we did a Med cruise to Marsilles, monte carlo, Florence, Pisa, Rome and Namples, the night before we went to Naples we were having dinner in the main dinning hall. Another couple asked our waiter what to expect when in Naples. he told us do not buy anything off people in the street. he told us a story that he bought his dad a radio from a street vendor and when he got back to his car he opened it up and it was just a brick in a box. He went back to the street vendor and started to complain. He said that one guy came from behind him and told him to mind his business or he will be dealt with.
Basicly he said that the Mafia still operates in Italy and naples is a big center due to the ports. We had a day excursion to Pompeii which was much better tha wealking around dirty Napoli.