How to convince a client that you will not steal his idea [closed]

Question

I came across a thread entitled How To Stop A Developer From Stealing Your Business Idea and i can't help but raise a brow. The issue talks about a developer being able to pass on the idea to another and benefit from it.

As a developer, what is the best way to assure your client that you will not steal his ideas? Are there any practices, laws or anything that takes care of the interests of both sides?

edit: linked to thread, and i didnt understand everything that was said