Summarize:

" There are tools you can use to research this for free online. For new cars, check out Edmund's TMV pricing.  For used cars, take a look at the Kelley Blue Book price. You can also use online tools such as US News Rankings and Reviews for cars and trucks to get a general idea of pricing from various dealerships in your area. Market value is determined by a number of factors, but essentially, the value is calculated based on the current automobile market as well as the price that dealers around the country are selling a particular car for. As a safe bet, make your "target price" roughly equal to the car's true value. Your target price is not an opening bid; on the contrary, it should be your closing bid, and the price you will not go above. If you feel a little more daring, you could make your target price $500 to $1000 less than true market value for new cars or 10% to 15% less for used cars. Getting a dealer to settle for this price can be extremely difficult, but it can be done. Before stepping foot in any given showroom to start negotiating, place a call to the dealerships in your area and inquire about their asking price for the car you're interested in. Do not mention anything about a trade-in, monthly payments, or financing. The only thing you need to know from each dealer is the out-the-door price. Car dealers make a good amount of profit on financing deals, which means that you might lose out if you rely on financing from the dealer. Apply for your own financing through a bank, credit union, or another lender before you head to the lot. One exception to this rule, however, would be if you want to take advantage of a special promotional interest rate offered by the dealership. Compare it to what you can get at your bank or credit union. The process of buying a car can take up a lot of energy and a lot of time, so if you want to put up a decent fight, you need to make sure that you can keep up with the salesperson throughout the entire negotiating process. As a general rule, you should also stop by when you have plenty of time and do not feel rushed. To the same end, you should avoid car shopping when you are in desperate need of a new or new-to-you car.
Find out the car's "true market value. Get quotes from multiple dealerships. Set up your own financing. Rest and eat before you go in.