An “official guide” is a professional provided with a high cultural level, certified by an University Degree which requires studying art, history, archeology, architecture, paintings, geography and other minor subjects.
Official guide means that you must pass a very hard exam, organized by the government, about all the monuments, churches, paintings, museums, gardens in the city where you are going to work. If you succeed, the government gives you a “license” to work as an official guide.
I’m recorded in Official Guide Palermo City List with the license number 096/082.
Italian laws about tourism are very severe, in order to protect tourists and to give them the best qualified operators. This is why unauthorized guides are fined by police as illegal operators, and even those tourists who book a non-official guide get fined too!
My advice is: ask your guide to show you his/her “Official Guide” license… then you’ll be in the right hands!