Background Information: I am working on putting together a sales
training presentation, and this is the first time I have been given
such a task. To achieve this I have already purchased the popular
sales training books and am going through them.

One thing I have noticed that almost all of the books do not have good
(some do not have any) information on "buyer psychology" and how to
harness that to a salesperson's benefit.

Question: What effect does human psychology have in the overall sales
process, overcoming objections from customers, and closing the sale
successfully and quickly? Also, are there any site that conduct
personality tests for free (they do not have to be very in depth just
simple versions would be good enough).

I am looking for resources that I can read and utilize to compile my
own presentation in this regard.

Google search of my key words left me quite unsatisfied, words I used:
a. too many fluff type document
b. Sales Training courses (I do not know how valuable they would be
when they try to cover everything under the sun in 2 hrs)
c. General PSYC 101 type information (i.e. Psychology has a lot of
part in business management and sales . . . but it does not connect
the dots).

Key words I used:
Sales Psychology,
Consumer Psychology,
Consumer Habits,
left brain / right brain customers,
Maslow's Needs pyramid in context of sales closing and sales presentation

Since I am not clear as to the exact answer for this question, here a few tips:

Answers must include links to articles, whitepapers, stories (case
studies), or simple information sites and must provide the information
that would help sales professionals understand - that all people are
not created equal psychologically (based on facts), people are
different and each should be treated differently (how to sell to left
brain Vs. right brain? How to sell to man vs. woman? Or how to sell to
baby-boomers vs. Gen X?).

Since I my self do not know what will be the exact 100% satisfying
answer to this question - I will set a bonus for $10 to $50. Bonus
would be assessed based on over all quality of answer, exactness, and
uniqueness (from what I already have) of the answer.