What power does the salesman have? None. He has cars, he wants to sell them. You have the money. You have the power.
He postures that he has the power but really, you can walk out at any time. There are other dealers, there are other kinds of cars, there are other sales guys at that dealer, and you can come back another day. Used cars maybe you don't see great deals all that much but on a new car, there will always be another car.
As a buyer, I want the seller to know two things to make a deal.
1) I'm serious about buying, and have the money/financing to buy TODAY. I can make a deal if he makes a deal. I don't HAVE to buy today, but I CAN. That makes a big difference. No one wants to quote a price that they can never match again, often times there are specific reasons why they can get a price at that moment but can't in general.
2) I'm not interested in the fine particulars. I want the best price. I will look at his lot and his competitors lot, and buy the car that is closest to what I want FOR THE BEST PRICE. Often they have inventory they are desperate to get rid of and will do it with 0 margin or at a loss just to get rid of the car.
An example, my last car was supposed to be $328 a month, but I paid $208 because I got the car in a dark gunmetal gray instead of the black I wanted, even though all the other features were the same no one wanted that color. I eventually grew to like it. I bounced between 3 dealers and they knew I had the cash, they knew I had the credit, and they knew I was flexible. Their initial offer was $250, I squeezed them down from there. If I had just faxed them like this article says I would have gotten nothing because it says I want black, and they didn't have the car in black. If you say you want the car in any color they aren't going to give you a good price because you sound flimsy.
Also as a note, never show one dealer another dealers quote. Tell him the number but NEVER show him the quote. You can cause serious problems for the original dealer and lose your deal. Often times you get these deals with things like the dealer getting a manufacturer rebate that you don't really qualify for but they can fudge some how. You play nice with the dealer, they will play nice for you.