I did personally use Kim San and he was fine. He was a little more personable than other tour guides (from what I could tell) and he used that ability once to get me into an attraction that had already closed. I recommended him to a colleague and he fobbed her off to a "contractor" guide. She didn't say the other guide was bad, but it was a surprise and nobody (including Kim San) told her. However, I've seen reports of other "reputable" guides doing the same thing. I guess they sometimes double or triple-book.

You might want to clarify this before you get there...