  I would highly recommend reading urlLink Confessions of a Car Salesman before attempting to set foot on the property housing a car dealership. It covers a lot of bases with tips and explanations to help you prevent yourself from getting completely screwed when it comes to buying a vehicle.
Other tips from my personal experience: 1) Show up with knowledge of the fleet, the price of your car, all rebates available, options and option prices of the vehicle you want. Have with you a printed wish list that explicitly states the Kelly Blue Book price of your car, how much you want for a trade, and how much you are willing to put in as a down payment. 2) Know your credit score and know how much the banks and credit unions are able to get you as an APR for financing. 3) Mark down additional things you want included such as cargo nets, fabric mats, extra keys and keyless entry remotes. These can often be worked into the deal or given to you for free. 4) If the dealer doesn't want to comply with these requests, write down the VIN number of the exact vehicle you want, and call every dealer within 100 miles asking them how much THEY want to sell you that car for.
Dealers will trade inventory in order to make a sale, and that can save you thousands of dollars! 5) DO NOT GIVE IN. Even if you have signed over the title and are all the way back into financing, when they try to screw you by saying, "Oh, well you only qualify for 9% APR, so sign here. " Just say, "Oh ok, then I'll just take my title back for my car, we'll cancel this sale and find another dealer who will get us the rate we want.
" I guarantee they will try harder and harder until they make the sale, because they will usually get fired if they don't. You HAVE to be ready to walk out that door, and make them realize you really will! I hope these tips from my experience will help another sucker (oops, I meant buyer! ) to get what they deserve! 
