Hope I'm not too late on this thread, but maybe this info can help someone. I had a brief stint in used car sales a few years ago, and learned quite a lot.
NEVER pay sticker. The average used car has a $3000-5000 mark up. Subtract $5000 and start your bidding there.
They will laugh and/or act insulted. "You can't be SERIOUS???!!!" Stand your ground and don't be afraid to state your position. There is nothing wrong with paying a fair price for a vehicle. Don't let them bully you.
The best time to buy a used car is the last Saturday of the month. It's quota time and the managers start getting nervous and are willing to cut a much better deal.
Shop around and don't buy the first one you see.
The first thing that you need to tell them is: I AM NOT BUYING TODAY. They will try to pressure you, ("what will it take to get your business today?"), but do not give in.
If you are financing, as about 95% of us are, get a loan approval on the outside first. That way you are now the equivalent of a cash buyer.
Buying a car is like playing poker: wear your heart on your sleeve and you're toast. Walk in, act nonchalant, tell them you are looking at several cars (which you really should, but regardless tell them this anyway even if it means only literally "looking" at ads on the Auto Trader), and be prepared to walk away.
Car salesman are taught to "take control" of the negotiation, starting with the way that they are taught to shake hands and not let go until you give up your full name, but guess what? YOU have the $$$. I live by the golden rule: he who has the gold makes the rules.
Visit this FREE website (to which I have no affiliation nor do I get anything from them) and LEARN about the business. What they hate most of all is an informed consumer.
CarBuyingTips.com
If you are replacing a car (and who past the age of 16 isn't?), then sell it yourself. In about 95% of trade-ins, the consumer gets ripped off.
Don't buy their BS add-ons, e.g. extended warranty, "dealer prep", "rust proofing", "fabric protection", etc. Warranty Direct (backed by GE) sells multiple levels of coverage and time/mileage, and will finance it for 12 months at ZERO interest. I have had two of their warranties, used both of them, and came out substantially ahead. Car Buying Tips covers this as well.
DO NOT EVER SURRENDER YOUR KEYS. That is the oldest trick in the book to keep you there. Keep your keys in your pocket. Ladies, leave your purse in the car. How many times do you need to apply make up at a car lot? I have seen salesman go so far as to hide car keys that a person left on the desk when the prospective buyer got up to get a Coke.
The person that can walk away wins. Don't fall for their con games: there is a guy coming to look at this car in 30 minutes, it goes to auction tomorrow, it's got a special price that goes up in 5 minutes/tomorrow/next week, etc.
Keep track of how long the car has been on the lot. Another trick is, "we just got this car two days ago and they never last, better get it while you can", for a car that's been on the lot for a month.
ALWAYS insist on a Car Fax report. If they refuse to provide it, then walk away.
When you've narrowed it down to what you think is "the car", get a mechanic to inspect the car on a lift. I once paid a professional appraiser to inspect a classic Corvette in another state, and paid him $100. With all of the missing items that the dealer had to put on the car (missing jack, head lamp bezels, wipers not working) he saved me over $500 versus what it would have cost me to fix. This was on a car in Cali that had been owned by a celebrity and was "completely maintained".
Do a Google search and find the "Black Book" price for the car. This is what dealers use at auctions, and usually they can beat that price. Edmunds is a good source. Kelly Blue Book is pure fiction.
Hope this helps.