Making a last minute decision to book a private guide, our hotel was able to arrange one for the next day. 

The next morning Unal greeted us with a warm smile which didn't fade during a cold and very wet January day. After a short discussion about the itinerary, Unal was happy to make changes on our request, and then we were off in a taxi to Hagia Sophia. As Unal introduced the main histories of the various sites we visited, he welcomed and handled all of our questions with an enthusiasm of someone who really loved his job.

We had a specific request for lunch, and Unal escorted us to the restaurant and offered to let us eat alone. However we were happy for him to join us and felt very comfortable sharing a meal  with him. It actualky allowed for a more interesting discussion beyond just tourist information.

Overall, I would recommend Unal as a friendly, warm and knowledgeable guide, as would look him up again if I returned to Istanbul.