Want prospective clients to trust you?
Act against your financial self-interest.
You might say to a prospective client who is not as ready as they think they are:
“Based on what you’re telling me, I don’t think a custom project is a great fit in your current situation. The upside for your business simply wouldn’t exceed the price. My advice would be to read my book, implement the recommendations you find there, and we can revisit a project engagement in six months.”
Of course, this sort of behavior isn’t really acting against your financial interests.
It’s only acting against your short-term financial interests.