This is a question I started pondering about 10 years ago as I began building a commissioning staff. I don't ponder it too much anymore, as I'm pretty sure I know the right combination of qualities, skill sets, and professional experiences. This confidence has come with its share of good picks and not-so-good picks, each one being a learning experience.
Before I start listing the top qualities, in my opinion, of a commissioning professional, I want to make it clear that I don't expect to find all of these in a single person. Even if one is lucky enough to find all of the non-technical qualities in one man or woman, it is impractical to expect a single person to have in-depth training, knowledge, and hands-on working experience with every type of technical system that might need to be commissioned. Therefore, many commissioning professionals will come as a team. It is best if every member of that team possesses most of the following qualities, especially if they are going to interact with the owner, designer, and contractor team members.