Yep They go to school to learn manipulative techniques (getting you to say "Yes," three times is one I've heard of) that are subtle and (in many cases) most effective. In the computer world read Fogg's work (From behavior design to addiction - The manipulation of our thoughts and behaviors has developed in social networks in part through the courses of B.J. FOGG).
Best approach is to study the marketplace carefully, determine what it is you would like to purchase, determine the best price you SHOULD be able to get it for, then find as many reliable sources for the object of your affections before getting in person at a dealership. With the Internet shopping is relatively easy. I sold my ride and bought a brand new vehicle via email from a dealer in another adjoining state the same day (buying at the end of the model year at the end of the month). Got all manner of options effectively for free.
If trading, I recommend a two step process. Don't drive your trade to negotiate the purchase. Negotiate the best price (and financing deal) you can. Get them to write it up ("can you put this in writing so I can be certain I understand all the charges and such - something WE can sign?") Once you get the papers in hand, ask to use their phone (or take out your cell and excuse yourself) to 'call my wife and explain the deal.' (if there are OCR copies, take one out of the middle and put it in your pocket. Call your answering machine - whatever - talk for a while - lots of "Yes Dear/Honey," ending with "OK, you're right, will do, see you shortly."
Then tell the Sales rep "She says OK, if I trade in my Hyundai Escape. Can I bring it in tomorrow (Saturday, whatever)?
OK, see you. Bye
Take the paperwork with you - need to go over it with Honey.
Then, when they re-write the deal with your trade, you will know exactly what they are willing to pay for your old ride. Lots of time this is a ridiculously low figure - but at least you'll know what it is and can decide to take it or walk, or buy the vehicle outright and sell your trade on your own. If you negotiated a financed deal, be sure to look over the items to be financed and the purchase price shown for the vehicle - because the dealer 'earns' on the financing itself, the price shown for the vehicle may be a bit less than you expected.
So, if you're a cash buyer, that's what you need to insist they sell it to you for.
They will, or they won't. You can walk - there are other dealers. If you're a wise buyer, you're looking for the less popular trim or model that didn't sell as well as the Super Chateau Mobile 2000 - all year year. One of the dozen they've still got on the back lot now that the new models have arrived.