Once, my friend said to me that in order to be a good salesman, you gotta learn it from the chaps in Petaling Street, Kuala Lumpur.
Regardless true or not, one has to see it to believe it. The way they promote their stuff, the way the reject your offer, they way they counter your offer and the way they give their final price, it is rather amazing to how they work their way to earn a living.
Anyway, one important point that a good salesman must not discard is to be courteous at all times. You must respect decisions made by customers regardless whether they are interested in the product you are promoting. Needless to say, it is how you present yourself that closes the deal rather than how great your product works.