Let them know how astute your are. Provide just the right amount of information to help your customer. Show your knowledge and expertise when they want it. Don't talk more than you listen. The more you get them to talk to you, the more quickly you can move toward being a solution finder.
True professionals are always busy working on significant work.
Make sure that you look and act like you are busy with good work. Respect your customer's time also. Whenever you can, make an appointment. That says you are serious and a professional. They make their own decisions.