Free greeter programs around the world encourage locals to welcome you to their hometown
Greeters are not licensed guides.
Greeters don't work for the tourist office.
Greeters are just outgoing locals in a particular city—9 in Italy alone, from Milan to Naples, Torino to Bologna (and, for that matter, Paris to London to New York to Melbourne)—who have banded together to offer their services, free of charge, as sort of free-ranging tourism ambassadors.
Sign up for a greeter program, and you will be paired with one of these local volunteers when you hit town.
Sometimes, their help is limited to a short session (15 minutes to half an hour) in which they show you the ropes: how the transit system works, where the best local place to grab a bite are, what's a good neighborhood just for strolling around, where can you find the best deals.
Sometimes, particularly gung-ho greeters will give you a two-hour guided tour.
Best of all, it's all entirely free.