Salespeople who are about to make a sale are often worried they're going to lose a sale, so their tendency is to say yes to whatever the customer asks. Obviously, that's not a profitable response, so a sales manager's job is to counsel the salesperson and keep them in the right frame of mind.
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.