Does it mean the person is lying? Or, does it mean that the person is really telling the truth?
Regarding, "I promise..." in Statement Analysis
Think of the speed of transmission of the brain choosing words, including these. The person has 25,000 words to choose from and wants to make a statement. In the answer, not only did the brain grab the words to answer the question, but extra words, (showing extra effort) were also chosen to add on to the answer.
This means not only extra effort, but more 'time' spent choosing words, making the answer very important to the person.
When we hear someone with the words "I promise" attached to an answer we must ask ourselves some questions about its use:
What topic caused the brain to grab those words?
Why this topic?
Why not other topics? (same question for figures of speech, including "Honest to God, Swear to God, Swear on my mother's grave..." and so on.)
It is a signal that the person is normally deceptive, or practices general deception. The person recognizes this about himself and now shows a need for emphasis in the response.
Now, as far as the topic:
The person really wants to be believed and knows that emphasis is needed, and this is for one of two reasons:
a. The person is truthful here, which is a rarity, in this specific topic, while other topics are dealt with deceptively;
b. The person is now being deceptive, about this topic, and is using the emphasis in an attempt to persuade rather than report truthfully.
Those who develop one of these habits of speech early in life should be dealt with in the same manner as above, noting what topics cause this habit to arise, and what topics do not.
Some people that are generally politely deceptive (about appearances, likes, dislikes, flatterers, and so on) will often develop this habit.
The problem is that even if they are not fabricators of reality, they are comfortable with deception, and deception, as a habit, is like an insatiable addiction:
it grows with time, and 'tolerance' against truth is built up with time, as success breeds success, and even in flattering, (false flattering) where the slight deception is met with a positive outcome, the flattering will increase in both use and intensity. The child grows into a "schmoozer" and can even become quite successful in sales.
Honest salesmen and women exist, but most of us can attest to critical situations in which sales professionals utilized deception in dealing with us.
In Statement Analysis' younger sister, "Analytical Interviewing", we find actual linguistic techniques that are effective in sales, and can increase both communication and sales results. These are effective techniques for social services as well.
Yet like much in life, illicit use can be evidenced by those who apply themselves to learning principle, and then apply it in a deceptive manner in order to facilitate self gain, including in sales and various manipulations.
I am currently constructing a training manual specifically designed for sales forces who wish to see honest gain.