1. Assume a commonality of interest that benefits both, and act towards it.
2. Accept that the best possible motive or interpretation of another's words or actions may be the true motive or interpretation, and act accordingly.
3. Question as need be. Ask only honest questions. An honest question is one for which you are prepared to accept more than your own answer.
As you can see, there's really only three of them. It was originally laid out as foundation, interpretation, question, action - later on it got up to as many as five or six points, but I think it works best as laid out here, with action tied to foundation, and with action tied to interpretation. There was originally a point about sincerity, about accepting the other may believe what they say is true - really this falls under point #2.
Also, it's kind of a joke to call these principles of Professionalism, at this point. They work even better for life in the encounters where you're not getting paid.