Intentional Use of the Palms to Deceive

Some people ask, 'If I tell a lie and keep my palms visible, will
people be more likely to believe me?' The answer is yes - and no.
If you tell an outright lie with your palms exposed, you might
still appear insincere to your listeners because many of the other
gestures that should also be visible when displaying honesty are
absent and the negative gestures used during lying will appear
and will be incongruent with the open palms. Con artists and
professional liars are people who have developed the special art
of making their non-verbal signals complement their verbal lies.
The more effectively the professional con artist can use the body
language of honesty when telling a lie, the better he is at his job.
Will you still love me when I'm old and grey?' she asked, palms
visible.'Not only will I love you,' he replied, 'I'll write to you.'

Palm Power
One of the least noticed, but most powerful, body signals is
given by the human palm when giving someone directions or
commands and in handshaking. When used in a certain way,
Palm Power invests its user with the power of silent authority.
There are three main palm command gestures: the Palm-Up
position, the Palm-Down position and the Palm-Closed- i
Finger-Pointed position. The differences of the three positions
are shown in this example: let's say that you ask someone to
pick up something and carry it to another location. We'll
assume that you use the same tone of voice, the same words
and facial expressions in each example, and that you change
only the position of your palm.
The palm facing up is used as a submissive, non-threatening
gesture, reminiscent of the pleading gesture of a street beggar
and, from an evolutionary perspective, shows the person holds
no weapons. The person being asked to move the item will not
feel they are being pressured into it and are unlikely to feel
threatened by your request. If you want someone to talk you
can use the Palm-Up as a 'handover' gesture to let them know
you expect them to talk and that you're ready to listen.
The Palm-Up gesture became modified over the centuries
and gestures like the Single-Palm-Raised-in-the-Air, the Palm-
Over-tbe-Heart and many other variations developed.