* Car salesman DoS attack the customer with numbers and options, for example using 4-square grid of options: overwhelm the customer with at least 4 different financing and trade in options, too many decisions to compare, lot of numbers, math, options, numbers, more options, overwhelm the customer, then steer them into the set of numbers that maximizes your commission.
* That amazing deal of the week advertised in the paper? Sorry, we don't have it anymore, we just sold the last one (bullshit) but this one here is similar model for just a little more (bullshit)
I read this article over 10 years ago, and it remains the gold standard of what you must read before stepping into a car dealership. Basically stand firm on what you will pay total and if they start playing these games then be prepared to walk away without the new car.
Also, even if it pisses them off, haggle and get prices from multiple dealerships, then play them off against each other. If they won't play, walk away to another dealer.
I'm not saying I got the best deal possible; I didn't shop dealerships. (OTOH I'm not sure that would have worked, as the model I was buying was in demand.) But basically, I think I did okay.
I'll probably go with TrueCar.com or something like that to automate the process next time, unless I get a Tesla.
I documented my experience at http://xn.pinkhamster.net/blog/misc/buying_an_audi_under_inv...
I still got ripped off, especially on the trade in--but my wife was rather pregnant and close to being put on bedrest at the time and we didn't want to have to deal with Craigslist or whatever for selling her old car.
I can do the math to figure out monthly payment for the price I what is at that point. Then I just negotiate using that number, if they bump up the trade allowance or reduce the price of the car it really doesn't matter. I precompute a few numbers to know where we are (e.g., Invoice, Invoice + 3%); but also know the cost of a $1 worth of financing so that I know how much they're charging me during a back and forth.