Tour guides: surely very knowledgeable, according to the Italian law they have to be licensed. That means that they have to get a permit to be tour guides through an oral and written exam many times very hard and peculiar. Tour guides are the only ones that can give explanation - territorially speaking - within the monuments or museums of interest. You can see them for example in the Sistine Chapel or in the Colosseum. They are normally the most expensive to be hired per hour.

Tour Escorts: according to the Italian law, they have to be licensed, too but the exam to get the permit is much easier. They cannot give explanations within the monuments. Their preparation and historical/cultural/art education is very high but they can just give explanation when on busses or minivans. Their job is more various: they follow groups basically everywhere and they take care of all bureaucratic things (check in/check out/ tickets/ meeting places, etc).

Tourist Interpreter: they have a lot of knowledge too, but their job is 100 % based on their language education. They are nothing more than linguistic mediator. To be a tourist interpreter you have to certify a certain level of education.

Driving Guides: this is a pretty new figure that operates in this field. Driving Guides are very expert drivers that show you around with those very fancy and cozy vehicles with a deep knowledge of the Italian History and Art. Almost all of them are perfect bilingual.

This is more or less what the Italian Tourist Legislation says. Obviously trespasser will be prosecuted with big fines or confiscation/revocation of their permit.