I do all kinds of research before booking excursions. If you are reading this you wont need to do the same work I did. As part of a cruise in May 2012, I contacted Nikos at http://www.privategreecetours.com/. Communications (from Canada) via email couldnt have been easier. Nikos offered one price for just my family (my wife and 19 & 13 year old kids) and another if I arranged for 10 people. It was easy to find 6 other people who wanted to join the tour via Cruise Critic. Nikos met us at the terminal and provided an excellent tour. He provided lots of personal insight and told us all we needed to know before getting to the various destinations to tour on our own. I listened in on other large group tours (as noted on other replies, the driver cannot provide the tours) and they were hearing the same information we had already heard. Nikos is extremely proud of his country and is happy to share his passion. His insights on timing, where to go for lunch, and places to see where the large impersonal group tours cant reach made for a fantastic day. I strongly recommend using the link above and book your tour. You really wont regret it.