I have purchased two vehicles in the last 2 months. This will be lengthy but it will be useful. I visited over 10 car dealerships in the process so take the time and read it.
First of all, I have heard every excuse, lie, story, etc., you could imagine. The key is to know what you are talking about. If you're doing a trade in, dont expect to get much for it. I have learned that trade ins are probably the most profitable method for car lots. I traded in my vehicle and got what I thought was a solid offer; however, I checked back a week later and they were *asking* $5000 more than what I traded it in for. Now I realize they didnt sell it for that, but I still thought that was a pretty dang high mark up.
This is very important- do not get lost on their offer sheets. I can promise you that you will see a sheet of paper with 4 boxes in the middle of it. They are going to write as many numbers in those boxes as you can imagine to try and confuse you. Also, take the time to calculate out what your payments will be overall. I know that sounds simple, but on their first offer I was going to end up paying $8,000 just to finance the car and pay for the title and "document fees"! And speaking of, their first offer will be absolutely terrible. They just aren't going to give you anything worthwhile on your first offer. They'll make it sound like their losing money on the offer you actually take, but trust me, they're not.
They love to extend the months of your loan to try and lower the monthly payment because most of them are stupid and think that they can convince you that they are giving the car away. Also, I made an offer on a vehicle and I told them I wouldnt buy it unless the APR was under 4% because I knew I had good credit. Well, he responded " oh yeah we're right there at that." Of course I said, "what do you mean?" What does "right there at it" equate to? Well, it turned out that it was 5.5% which would have made about a $1500 difference in how much I would have paid for the vehicle. So make sure you have concrete numbers; if you say you wont buy it unless you have ____% financing then dont budge. Obviously, that'll be up to you and your credit.
One salesmen made an offer to me and informed me that even he couldnt buy the vehicle for that amount. Which. is. absolute. bull. crap.
I strongly recommend not buying a vehicle after one visit to the dealership. People get lost in the euphoria of smelling the leather and imagining how much more smooth the drive is in that new vehicle. You need to leave the dealership and think on it for 24 hours. They'll hold it for you for that long, trust me. But they're not going to want you to leave without signing a deal. Their number one rule is to not let the customer leave the lot, so dont expect your visit to be a quick one. It will take you a while because when you say your leaving they'll bring out their sales manager, and then when you tell him you're leaving they'll bring out their general manager, and if you still are trying to leave there is a chance that there's another suit you've yet to meet but that you need to meet before you leave.