I can also suggest one caveat to beware:
The "belittling" factor.
Example:
Car costs $10,000. You decide beforehand that it's really worth $8,000 and that's what you want to pay. You go to salesperson (who never gives you answer really, but wants you to "step inside) who then hears your offer.
He laughs. He belittles. He questions your "ability" to understand car economics.
His job is to BREAK you down. Accept HIS reality, not YOUR reality. QUESTION your facts. He'll go down a whopping $200. So it's $9800. His job is to make you believe he CAN'T go down at all. That you'll get the SAME price elsewhere. This car is WORTH it.
These guys are MASTERS at the mind game. If he has to sit for an HOUR to wait it out, just to make the extra $1,000 profit -- bet your ASS he'll do it (if he KNOWS that you are serious about buying, and it's just a matter of figuring out the price).
Unless yo'ure damn good at mind games back at someone -- you'll probably lose. These guys do this shit day in/day out.
So HOW do you avoid the dreaded negotiation, and belittling and arguing back and forth where they fight for an hour to go down $50, and you're still $3000 away from *their* price and they're making it seem YOU are the one who isn't being 'realistic'?
Walk.
Put the leverage in your corner. When they sense that you WILL walk and go try your luck elsewhere -- comes the leverage. Stop answering their rhetorical "questions"

"But Cindy DON'T you like this car?" "Don't you agree, it's beautiful?", "have you EVER had problems with this model before? It's WORTH it!" blah blah).
Treat it like a professional business meeting. Act like a lawyer. Make your case, present it and say THAT'S it. If they can't reach it -- make your best offer, and you'll take it back and sit on it. You're NOT going to sit there for an hour so they can *convince* you. You just want their BEST offer and that's what you're WAITING for.
Trust me. Making a stand and STICKING to it si *much* easier than playing a battle of wits game with a sales person. WAY easier.