Unqualified guiding is not permitted by the Italian Law.
Therefore, when booking a local guide in any Italian city, it is your right to ask for proof that he or she holds a license before closing any deal. Under present regulations in Italy, as in most European countries, there is no such thing as a "docent", "lecturer", "art historian" or "cultural association" to deal with when hiring the services of a local guide, either directly or through travel agents. Licensed Tourist Guides are the only professionals permitted to conduct tours in all sites and museums within a city.
To become a Licensed Tourist Guide in Italy - like in most EU countries - candidates must pass an examination given by the local public tourist authorities to assess and test their knowledge of the city in terms of its history and geography, its art and architecture, its museums and art galleries, churches, its environs and cultural features. As part of the requirements, candidates must also prove their knowledge of each of the foreign languages they applied for with oral and written tests.