Be sure to distinguish between tour guides and tour drivers. You can think of a tour guide as an individual licensed to take you around a historic centre AND INTO the museums and so on. For that kind of tour, you would want a local guide. Indeed, most of them are licensed for one town only. Touring Chianti or the Cinqueterre, for example, you would probably be looking at a tour drivers who can take you to wineries, villages etc., providing a commentary, but who CANNOT take you into museums and similar. The big tour operators - pullman bus rather than minibus van - have a driver who just drives and a tour guide licensed to conduct the tour.