I wouldn't call it wisdom, just having worked on the other side, but here goes.

First thing: salespeople never control the price numbers, the managers do. But it's to your advantage to go through a salesperson because if a manager sees a salesperson work a deal properly at a lower number, they'll do the deal, as opposed to if the customer is a pain in the ass and gets the manager directly involved, they'll be less flexible.

Let's say you go to a dealer, you pick out a car you like, you drive it, do whatever else, and decide to buy it. The salsperson sits you down, offers you a soda, and starts the paperwork. The first thing they're gonna want you to do is make an offer. Don't say something like, "give me your absolute lowest number," because the salesperson doesn't know what that is and you're doing something that doesn't fall within their standard process they have to follow. Anything that you do to take the salesperson off process doesn't really help you get a lower price, but it does help you spend more time in the dealership than you have to. So this is why I recommend buying the car in 2 trips. First trip is your reconnaissance mission to make sure this is the specific car you want to buy, and you write down all the option codes on it, any dealer accessories, etc.

Go anywhere that's not the dealer where you can get internet access and price out the car on any of the internet sites out there that list invoice prices. I particularly like edmunds.com because when you put in your zip code it'll tell you about any incentives on the car and what other people in your area have been getting the car for on average. You then know what the invoice price is. Make sure you have your total invoice price including the freight charge, because that's gonna be charged no matter what.

Armed with this knowledge, you go back to the dealer. Can be just a couple hours later, can be a couple days later, whatever. If you've decided to pull the trigger and have the invoice price, just go back real soon. This gives a sign that you're serious about making a purchase. Now you can make an offer to the salesperson like they wanted you to do before. Don't bring a printout from Edmunds or wherever, just know that number in your head. Don't tell em you know the invoice price or anything else, just tell em some number that's a good deal (I usually say $1500) below the invoice price. They'll write up a form called a buyer's order which has all the info on the car, the sticker price, and your initial offer on it. The salesperson's gonna give you the song and dance about that's so low, blah blah blah, tell em that's what you'd like to pay ideally, you might be flexible, and you just want to see if your number is possible. They'll probably ask you for a deposit, or to fill out a credit application, or both. Give em a deposit, but tell em just to hold the check and don't put it in their account just yet. Let em take the credit application but tell em to not run the credit. This way you're giving more buying signs, but you haven't had any money out of your checking account or a hit on your credit record.

The next thing the salesperson is going to do is give your deposit to the people who handle the checks, and show your filled out credit application (without the credit check being run) and buyers order to the manager. The manager's gonna laugh at your ridiculously low initial offer, and the salesman will tell the manager you said you're flexible. The manager will make a counter-offer with something like 500 bucks off sticker, and tell the salesperson to go back to you. They'll come back with the manager's offer on the buyer's order and say this is the best they can do. Your reaction should be, "well they obviously don't want to do my ideal number." The salesperson is gonna try and sell you on the higher number, but really they're only looking for you to make a higher offer. You can bump up your initial offer by 500 bucks or something. More goin back and forth with the manager, you might have to allow yourself to get bumped by 500 bucks one or two more times, but then you're right at invoice price.

Once you agree on a price, they'll need to run your credit and deposit the check you gave em before, and it's off to the finance office. I didn't work finance so all I can tell you is if you know what car you're gonna buy, get preapproved by a couple outside sources like a bank or a credit union so when the finance guy tries to dick you over on the interest rate you can show him the preapproval sheets from wherever else, and increase your bargaining power. Then if the finance guy can't meet or beat your preapproved rate, you just go with the preapproved one.

Don't buy any extended warranty that costs more than 200 bucks, never ever ever ever buy any sort of dealer maintenance plan, or any other extras that they try and sell you after you agree on the price of the vehicle.