What is the best way to deal with a difficult customer who has high expectations but fails to see their roles in making a project a success?

The best way to understand customer need is talk to the customer and try to dig out what exact he/she wants.

Project outcomes sjould be finalized and approved by the customer at the project charter's stage ensuring that any scope changes will affect the prject negatively. I found that staged delivery offers a great help in managing customers' expectations.

This happens only if the person is definite about the target but having no clarity about the path to choose. This can be solved with a discussion in which two way idea exchange is possible..