Everybody wants to “eat healthy”; but not everyone knows how to make that a reality, or in fact, what that really means. A food diary is probably the best tool for tracking everything that goes into one’s mouth (that is, assuming he/she is honest in actually writing everything down!).
When it comes to eating, I think most people are motivated by how they feel; if they feel like crap after eating something, it make take a while, but they’ll eventually stop (if they don’t, they have only themselves to answer to).
Ultimately, the key is to build a strong, nutrient-dense, and delicious base on which to live a healthy, energetic, and happy life. I would refer a client to a registered dietician/ nutritionist if they needed more than just basic advice.