If you can, bring a friend who happens to be a lawyer (a GOOD lawyer [;)]) with you.
Why?
I went with my father one day, to check out new jeeps. My Durango R/T was nearing the 30k mile mark, I had heard that their rear ends tend to self-destruct around 32k, and I had had the thing less than a year. Oh, and I was throwing away over $100/week in gas for it, as I commuted to work. Loved the thing, but too damn expensive for me. Already had a couple major repairs to it as well by this point. (All warantee work, but...)
Never mind I'm stoned out on percocet; I had my wisdom teeth taken out the week earlier, and 2 of them dry-socketed. I'm sure many of you know the pain that entails, and why I was taking percocet like kids take jelly beans.
So, there I am, with Dad. We're looking at jeeps. I had a Wrangler previously, and figured it's time to go back to basics. We've largly always been a jeep family; he had his Cherokee.
Me, I'm dumbed out and by the time we finish touring the lot, the percocet's wearing off; I'm hurting. I need to get a car, and NOW, before I lose my mind. The salesman saw this on me. Dad goes his own route...he wants one of those new Libertys.
I haggle for a bit, get a decent price on my Durango, get a not-bad interest rate..I don't care, I'll sign, shut the fuck up and get me the paperwork.
Dad?
2 hours later, he haggles the saleswoman (who looked like she had ironed out the entire charter to NATO) down to no interest, major money for the cherokee, and below cost on the liberty. He just LOVES to haggle. Holy Christ. "WHADDYA MEAN, %3.9 INTEREST?!?! I GET BETTER RATES FROM MY LOANSHARK!"...crap like that. Not above making scenes, not above flat out changing his mind. The man's a freaking artist at getting his way when it comes to car dealerships.
And yah. He's a lawyer. I know several others, some even around my age (shy of 30). They live for making that impossible deal in their favor.
If it's your first car? Don't go without backup, a lawyer as above. (Until that jeep, I had always gotten cars from my local dealership; their owner and my Dad go way back, so any screwing they'll give me, I know I'll get back in maintaince, warantee, and just repeat business. One hand washes the other.)