Trust is a critical element in the selling environment of today. In fact, we frequently reference what we call "The Mighty Wall of Mistrust" when helping clients develop new campaigns.
The concept is that separating you from your customer is a wall of mistrust - made up of anxiety, skepticism, doubt, fear, uncertainty, and the like.
This is perhaps one of the best marketing secrets I've learned. It's so simple - but as a rule, it is violated constantly.
It's such a big problem, that by simply following this rule, you will be far ahead of most of your competitors (if not all of them).