I don't generally worry about giving out too much information
The service I sell is not the plan, but rather the wisdom, intuition, and experience that I bring to the project. The plan hardly ever goes without a hitch, so you sell the fact that you'll see it through where others might fail. Yes, their plan was definitely scoped and defined well, but they still ran into unforeseen difficulties. It was their ability to make tactical decisions that saved the project.