Reading the top parent of this thread was very interesting because he was thinking in exactly the way I had been conditioned to think at that time in my life.
When a person in your life lies to you or manipulates you, you will certainly begin to question the value of other interactions from that person. Once you have confirmed that the person has a personality type that makes them particularly likely to lie or manipulate (compulsive liars, psychopaths, criminals, what have you), you must be careful about your interpretation of any communication. But here's the real difficulty: If a psychopath is trying to manipulate you and knows that you are conscious of it, the manipulations morph. They adapt to your particular defense. In the institutional setting, they're in it for the long haul so they don't mind missing a couple times. In fact, getting caught is often part of the manipulation.
I wandered off my initial topic here so I better wrap it up.