The 5 day tour of Sicily was very good overall. For me the highlight was to be Syracuse, the site of Athens defeat in the Peloponnesian war.
I have read Thucydides (in the original) and am an academic (though not a Hellenist). When the tour guide assured me that Greek temples were not painted I had to walk away and visit the site as best as I could on my own. Unfortunately, never expecting to find such incompetence, I had not studied the site myself and the signs (in Italian) are extremely basic, to the extent there is any signage at all. I have asked Viator for partial credit for the day in Syracuse.
I will return having studied the site myself. Their tour of the Vatican (cost me and my wife over$200) was ok except that the guide did not actually know English. She had apparently memorized a translation of her Italian language tour. She could not understand a word I said.
I speak standard Hollywood English, not some Yorkshire dialect. Unfortunately it is my nature to have questions about many things. I could have asked my questions in Italian but I do not know the right technical terms in Italian (only English and French). Again I have asked for a partial refund and have heard nothing back.
Viator seems to take the attitude that if someone has a license we will use him or her. Unfortunately whoever gives out licenses in Italy must be bribable or incompetent.
Reviewer is in unhappy mood. jrobbart is quite happy with easy to book and stated that there is a room for improvement of some of the guides. Please immediately contact the author of this review to discuss "no quality control of guides whatsoever" of viator tour. Viator needs to offer any options to resolve the issue according to poster's claims.