Who do you usually do business with? That's an easy question to answer: someone you trust. How does a business earn your trust? A number a reasons: you've done business with them before, you've been referred by someone you already trust, and/or they are a well known company (chain or big-box stores). But when would you do business with someone you know nothing about? If a business was to open up their books and show you exactly what they're doing, how much money they're making, what every employee gets paid, and what their plan is for the future then you would probably give them some trust. I'm not saying that many private companies go nearly that far, but what I am saying is that you tend to trust companies when they are transparent.
Whenever I go about designing a website for someone, or helping a client with search engine optimization, I try to give them as much information as possible. I like to put the power in their hands so that they know what they're paying for, and, if they would rather do it themselves in the future, they can. You may think that's crazy, but I usually find that a client would rather spend time working in their profession than in mine.
I don't believe in SEO or web design "secrets". The information is freely available to all know how to Google. Not giving a client certain information because you want to protect your job only breeds suspicion. When you are transparent and show them everything you know they're more likely to keep coming back and refer you to others in the future.