R-E-S-P-E-C-T

Aretha Franklin made these letters famous in her song of the same name.  It's a good subject for a discussion in sales.
Several years ago, I was working a booth, helping a business owner at a trade show.  During a lull in the trade show action he confided in me that he really didn't "like" his customers.  He felt that he was too well educated--"better" than his customers--after all, he owned a business, was college educated, etc., etc. . I thought to myself, during this discussion, this guy's not going to be in business in five years.  I way overestimated; he closed his business a year later.
He thought he was smarter than his customers.  He wasn't.  A good salesperson has to RESPECT his customers.  If you don't respect your customers--respect them for what they have achieved, for their own capabilities, for who they are, you cannot sell them anything.
From the moment you come into contact with a customer, that customer is evaluating you, testing you.  If you think you're the smartest person in the room, the customer will sense this lack of respect and your chances of getting the order is reduced geometrically.
If you can't respect your customers, you are in the wrong business.  If you can look at a customer and realize--really realize--the value in this customer, then you will be successful as a salesperson. Product knowledge is the easy part; respecting your customers can be difficult.  But it is absolutely essential to the success of a salesperson.