Just returned from a 10 day to Italy. Half was spent in Cava de'tirreni and the surrounding area. We visited Vietri del Mare, Sorrento, Pompeii and Paestum. My advice is not to count on local tabachi stores for train tickets. The train station is best and to buy round trip tickets to where you're going. Make sure you check the schedules on the wall of each station for the last train going back. The folks in Paestum said they didn't have tickets and were casual about not having them. Luckily the ticket machine in the station began working and we were able to get back to our hotel. Most of our tickets were never punched or taken but always get one in case the conductor decides to check you.
Nevertheless, the region is beautiful, people were gracious and helpful and the food and wine is fantastic.