First you take it for a test drive, and even get it inspected if you like (about 70 buck at Pep Boys). Then when you come back, you start rattling off all the problems it has. And if the dealer is not hard up for cash, then he may be willing to come down to Earth for a little bit. Point out EVERYTHING. Any creases in the leather, any door dings, any curb rash, and anything else you can think of. Make sure that you dominate the conversation. Then if you're lucky he might say "so what are you offering?" Then you have him. Offer him 4 grand, then let him respond with 5 grand. Then you respond with a final offer, "Okay, but it has to be final drive-out." This will make him think you're accepting his offer, but you're still going down by a couple hundred bucks.
Or be quick and fast and come out and say in a "cool" manner, "I'll give you 5 grand total drive-out."
Being so quick, he'll probably accept, since it's not outrageously low (only 1000 below asking price). Just be in control at all times, and don't let the dealer think he can push you around or give you BS. Throw out an offer that's low enough that he might accept, but not too low. Otherwise, he'll know you're lowballing him, and he'll know you have more money.
You basically have to understand that dealers severely mark up their cars above what they think they're worth. They do this to make money, but also because they know people will haggle them down. A buyer can just about always get the price down by some amount, even if it's just TTL and fees, and nobody (nobody smart anyways) pays sticker on a used car. One other tip, I would highly suggest you have the car inspected (it's worth the 70 bucks), as "Honest Johns" will commonly undervalue problems. Like for me a "simple AC recharge" turned out to be a bad compressor. Or "just needs new brake pads" turned out to be "needs a master cylinder and brake lines." Hope the sale goes through well.
Greg