Rule 1 is wrong!!!! Is Right
Having played the role of both PM and customer in a few large and small scale development efforts for a large North American exchange, I know that rule one is know the source of the requirements and to consult with them often. Negotiating deliverables and setting expectations is the only way to deliver a product that will make the customer happy. When possible have the developers meet with the source to ask questions and better understand the mission and goal of the project. Let the Operations crew have a peak at what's coming down the pike and get some requirements from them too.