We and two other couples spent three days in Santorini in early October. We had arranged with Santorini Experts for private tours on two of those days, and were fortunate enough to meet Marcos! He was a wonderful tour guide - knowledgeable, friendly, personable, and passionate! He optimized the time we had to see quite a bit of Santorini - not only the traditional highlights but also many of the more local aspects of Santorini. We thoroughly enjoyed our time with him, and learned and saw a lot!
I would highly recommend him, and Santorini Experts, to anyone who is going to visit Santorini!