You're opening a can of worms here. . .
Yes, there are psychological techniques that can be used in order to gain advantage in negotiations, some of which stray into the grey areas when it comes to morality & ethics; then again, in today's world no one seems to think a thing about taking cruel advantage of others when it comes to personal gain or company prosperity (I'll not get into current headlines to this regard). But yes, I have used certain principles in order to get the better deal, one such technique will be noted in a book that's coming out in the next month or so (not my book but someone else of note). I regularly use deception in a way that encourages people to assume that I'm genuinely gifted as a Psychic because that is the role I play as a performer. Technically speaking, this is manipulation that lends to me an advantage; mostly when it comes to reputation not so much financial (sad to say) but then, I don't push things as I probably could.
Here's the thing, unless you have a considerable level of training and field experience, the techniques you've learned aren't going to take you very far and can in fact, backfire on you. . . especially when it comes to car sales; those old dogs know more than a few tricks, even if they've only been selling for a year or two. Care, Funerary & Insurance sales are cut throat and they take no prisoners so a cheribum faced kid fresh out of high school is more than likely to be eaten alive. Especially if he's trying some rudimentary psychology on such people. Your best bet is to get your father or someone older that knows cars and how to conduct business (in cases of the apartment, etc. ) to side with you, advise you and play mediator.
Save what you've studied and learned (are still learning) for when you're a bit older and more mature. That doesn't mean you can't experiment with it and test things out -- you should! But it takes time and such experience to make such an approach "natural", which is the point.
I would strongly recommend that you check out "
How to Win Friends & Influence People" and books like Elliot Aronson's "
Everyday Mind Reading" and "
How to Read a Persona Like a Book" by Gerald Nierenberg. Then, after you've spent a while learning how to size folks up you can start down the paths of NLP and FACS which will get you much closer to the "goal" you seem to have.
Best of luck!