Have a bottom-line price in mind.

Have a bottom-line price in mind. Negotiate like this: "Salesman, I'll give you three chances to come up with a price I want. I did my research and I think I have a fair price in mind. Offer me a the lowest price you can on this car. If it's too high, I'll tell you. If you still haven't reached my price by third attempt, I leave. Ready?" Obviously, this only works if you really do have a reasonable price in mind. :) So do your research!