To me, the most important quality of a successful sales representative is the ability to have confidence in yourself and what product you are bringing to your people. You wouldn't buy anything from someone you felt like did not believe 100% in what they were selling you themselves. You don't want to be weak or passive about it, but you don't want to be overly aggressive. You want to sound like you 100% believe in what you are selling. If you are selling something, you should believe in that 100%, no questions asked. That's the most important thing, I believe, to make yourself successful. As long as you believe in what you're doing, the next person will believe.