SIN #3: Being an adversary, not an ally. Since customers are risking their career doing business with you, they expects you to represent their best interests. Phone Sin: Not asking the right questions to determine their interests so that you can be that ally and not a voice!
In my travels I find that the weakest skill that any sales person possesses is the ability to ask the right question. They know Features and Benefits they think they are asking questions to generate information but really they are fact finding with a view to closing for the sale.
Closing too soon. Not knowing your 2.0 Customer's strengths and weaknesses and not caring about building that relationship can make you an adversary very quickly.