In fact, manipulative people will (like a Trojan Horse) utilize a good person's credulity, his tendency to focus on reality and whether the words are true. The truth-orientation is what the good man does in his own mind when thoughts occur to him. But that is not the mindset of a manipulator. The manipulator seeks to use his victim's honesty against him.
A manipulator may wish to distract you. If an accountant who is cooking the books sees your eye moving toward the table of figures which evidences his sleight of hand, and then suddenly points at the model ship on the windowsill, talking about the painstaking work put into constructing it—the exchange is not about the ship. To “take the statement at face value” is something like autism. If you don't grasp this kind of misdirection, you need to study more literature.
A manipulator may simply wish to hurt your feelings. When a vindictive woman says to her ex, “You are terrible in bed,” she is not saying it as a sincere, carefully exact statement of what she thinks is true. She is saying it for an emotional purpose: to hurt the man, to attack his masculinity, to make him doubt his prior confidence and question whether his feeling of success with the woman was a sham. To impartially consider whether the statement is true or not is context-dropping. It should not even be considered in terms of truth analysis. It is not within the field of knowledge statements; it is in the field of manipulative statements.
There are many possible manipulative purposes, many reasons that a person might say something which are not plain assertions of truth: establishing social dominance, self-flattery, controlling you or gaining power over you, hurting your feelings, distracting you, disarming you or getting your guard down, winning you over toward some person or course of action.
Consider this exchange from the movie Star Trek: First Contact.
"BORG QUEEN: We, too, are on a quest to better ourselves, evolving toward a state of perfection.
DATA: Forgive me; the Borg do not evolve. They conquer.
BORG QUEEN: By assimilating other beings into our collective, we are bringing them closer to perfection.
DATA: Somehow, I question your motives."
The same statement (“we are on a quest to better ourselves”)—exactly the same words—have an opposite status depending on whether they are presented as a straightforward communication, or for a manipulative purpose. Here, the Queen does not speak with the purpose of sincerely communicating something she thinks is true. Her words have an opposite status: they are deceptive. She seeks to present herself as a noble idealist, hiding her evil motives; this is for her own self-deception, and by extension for the deception of others in order to control them.
In the case of outright lies, the difference between truth-communication and manipulation becomes apparent even to the credulous. For example, it is obvious from its content that the “Patriot” Act is the opposite of patriotic; it is clear that the title is a plain lie, made for a deceptive and manipulative purpose.
But every effective and cunning liar knows that he can only make his lie convincing by mixing it with some truth, thus giving the idea traction in the mind of the gullible honest man. This is where truth-seekers need to up their game. It is not proper to “take the statement at face value” and test it against reality, as though it is within the sphere of sincere thought, when the statement has nothing to do with what is true or false, and everything to do with steering your emotions and mindset.
How do you know that a statement is made for a manipulative purpose rather than plain, uncomplicated communication of thought?
You ask: “Why is this person making this particular statement at this time?”
Notice that truth-status is timeless and universal. “2+2=4” considered from the point of view of truth, is an eternal fact which holds for everyone. But that doesn't mean that every time someone says “2+2=4” he is expressing the truth; he may be trying to lend credibility to a load of BS, he may be distracting you, or deliberately toying with your perception of reality, etc.
An analysis of the truth of a statement does not itself take into account whether the purpose of the speaker was to communicate truth. But the purpose and intention and motivation of the speaker is part of the context of the statement. Analyzing this—which is particular to this speaker speaking to you at this time in this particular situation—is essential to understanding what is going on.
“Somehow, I question your motives”—that is the proper motto of a thinker who lives not a world of purely abstract, Platonic truths, but in the real world of embodied human communication. It does not mean that there is no such thing as the truth. It means that part of the truth, part of reality, is the speaker's motivation. Nor does this mean that you must be paranoid. You should be realistically skeptical and critical, as a continuous mental setting.
This is not cynicism or expecting evil. It is approaching reality without prior preconception about a speaker's motives, and without projecting your own motivation onto them. And then, the speaker's motives are judged for being whatever they are, whatever they reveal themselves to be.
You often get your first clue about manipulative purposes from your gut. Something feels off—which is an inkling or impression of some elements which don't fit. If you reflect on them later, you can sort out what was going on. But remember that the manipulator knows that in time your logic will sort it out. Therefore he controls the pacing and course of interaction to avoid letting your process of logical analysis operate. He will distract you, make you feel good by flattering you, etc. This is why the skill of analyzing motivation in real-time is crucial to sanity and success in real life.
It is not improper to take into account the speaker's motive, as a fundamental matter of the epistemological status of the statement. This is a process of getting more information, a larger and more comprehensive data set. Motive is not an “illogical” or “irrelevant” consideration. To dismiss motivation in this way is an autistic, fractured, narrow-minded and biased way of thinking. It will make you think that people are unintelligible, when in fact they are quite intelligible, even when they are being irrational and deceptive. Because you can identify their motive. The speaker's motive is the causal explanation of the statement.
Even good people must be cognizant of Machiavellian purposes. Because good people live in a world that is as messy as everyone else. But good people have the capacity to make sense of it.