Don't negotiate. Tell the salesperson and sales manager that you'll sign the paperwork the minute they hit your target figure. Politely decline any counter-offers, give them your phone number, and leave.
I used to sell vehicles from 2005-2007. I was the #2 top selling salesperson at both of the stores of where I worked. When I was working at a high volume dealership, I was averaging about 23 vehicle sales a month.
While it's true that getting a good price is a big part of the hunt, the biggest, most important, super-secret strategy to turn the stealth hunter (them) into the prey: stand tough and fight to maximize your dollar throughout the process.