Lacking honesty, either overtly or through omission

Deceitful, deceptive, disingenuous, false, untruthful

Living in an environment of distrust, crime, violence, or abuse
Idolizing role models who embraced trickery or lying
Holding a position of power where dishonesty results in reward
Desiring to keep peace through any means
Substance abuse
Self-centeredness
A lack of empathy
A fear of what the truth will bring
Believing that one's lies will never be discovered

Lying or cheating to avoid consequences
Telling one thing to one person and another to someone else in an effort to maintain friendships
“Misremembering” events in a way that will benefit oneself
Exaggerating to get a bigger response
Saying whatever it takes to get what one wants
Leaving out details that would negatively influence the listener
Not correcting someone's misinterpretation of the facts
Doing and saying things to put up a false front
Using compliments to distract or pump someone up, making them less wary
Claiming someone else's idea as one's own
Using manipulation when one's honesty is questioned
Denial; refusing to admit that one has lied
Compounding lies to maintain one's original untruth
Enlisting others to back up one's stories
Portraying false emotions to achieve a desired effect (fake tears, anger, excitement, etc.)
Lying to spare people's feelings
Lying easily, without any of the usual tells
Thinking before answering or committing to a course of action
An aptitude for reading the body language of others and judging their moods and emotions
Voicing excitement about things that one is not interested in
Giving very few details in order to better remember the lies one has told
Voicing some truth so the lie will go undetected
Checking to see if one's lie has been discovered
Avoiding eye contact, changing the subject, shifting about
Speaking quickly and asking questions in an attempt to change the subject
Downplaying the situation so others don't become concerned when they should be
Making excuses or laughing something off as if it's a joke
Eliciting sympathy in order to exit gracefully: "I should go; my mom's been pretty sick."
Carefully choosing what personal information one shares with others
Telling people what they want to hear instead of revealing one's true opinions
Having a backup plan or cover story in case one's dishonest actions are discovered
Avoiding pointed questions
Couching one's answers: "I honestly don't remember," or "I can't be sure."

DESPERATION, GUILT, INDIFFERENCE, INSECURITY, REGRET, SHAME, SUSPICION, UNEASE

There's a certain reliability with dishonest characters because they can be counted on to act in an untrustworthy manner. They can often be bought and will remain loyal as long as there's something in it for them. Because they can be swayed to do things that honest people wouldn't, a character who embraces dishonesty might do the dirty work on the hero's behalf.

An inability to trust others creates barriers, making it difficult for dishonest characters to acquire close friends and have meaningful relationships. They also may become scapegoats because of the mistrust of others. If they are directly involved in a situation with conflicting viewpoints, the person known for dishonesty will always be devalued against anyone else.

Fletcher Reede (Liar Liar) lies to everyone. He lies to his co-workers, the police, his mother, his secretary, and even to his five-year-old son. It gets so bad that when Fletcher breaks his promise to attend his son's party, the boy makes a birthday wish that his dad would no longer be able to tell lies. The wish comes true, showing Fletcher how far-reaching his dishonesty has become. Other Examples from Literature: Pinocchio (Pinocchio), Jay Gatsby (The Great Gatsby)

The best way to cure a dishonest character is to have him caught in his lies. The bigger the lie and the more influential/important the person is who discovers the untruth, the stronger the effect will be on the dishonest character. Another angle would be to show a different reaction to the lie than what the character expects (disappointment rather than rage; empathy rather than disgust, etc.). The surprise and relief may create the epiphany that dishonesty is heavier than the freedom of truth.

HONEST, HONORABLE, GENEROUS, GULLIBLE, JUST, RESPONSIBLE, VINDICTIVE