i'm interested in a 4 hour tour (private) of Salzburg any suggestions as to who may be good to chose from?
You probably need to provide more info. Do you want a more general tour of Salzburg or something related to SOM? I am typically one that does not do tours, and definitely not kitschy tours, but I did really like the SOM tour we did with Panoramic. In terms of the older part of town, I toured on my own with help from the RS guide.
This is the website that the Austrian Tourism Office provides for licensed guides in Salzburg: