In Friday’s poll, we asked how you thought car salesmen make their money. Nearly half of those who responded as of Monday evening said they thought it was through selling trade-ins. In fact, as a shopper, you stand to lose the most money at the financing desk. That’s the backroom – the business office you’re taken to after you shake hands with the dealer on the lot. This is the most important part of the process for the customer because it’s where features, taxes and insurance packages are cobbled together in an effort to get you to pay for more than you need (or want).

It’s a game of psychological warfare, said one current car dealer “money man,” whose identity On the Money kept private. These salesmen are looking for customers who are “as dumb as possible,” he said.

The bottom line for customers is that they don’t have to buy anything that’s offered in the finance office of the dealership, added John Linkov, the managing editor of Consumer Reports. He offered these tips:

-The interest rate you pay on a car is based on your credit score, so take the time to check it before you walk in the door. The higher the score, the lower your rate is going to be.

-Do your due diligence with your bank before hand. Find out the rate it will approve and have that rate in hand to negotiate at the dealer’s finance office.

-Don’t let the dealer or his money man get you into what they call a “yes mode.” Know exactly what you want in the car ahead of time and research the different options and packages so you don’t feel pressured to agree to someone on the spot (many carmakers now let you “build” the car you want on their web sites).

-Always negotiate the price of the car, not the monthly payments. It’s easy to get tricked into paying lower monthly payments if the loan is over five or six years instead of the customary three. Linkov recommends people stick to 36-month leases and nothing more.