I've found con artists and pathological liars to be two different sorts of people. That's just my assessment--I don't have any formal education or training in the topic, although I've known plenty of both.
The con artist starts by identifying the "mark," and from that point forward has only their victimization as a goal. The con artist will tell them anything and finesse, humor, flatter, embarrass, frighten or coerce them into doing what is required for the con artist to get their reward. They know they are lying, and they're very good at it. These tend to be very bright people, as it takes a pretty good mind to manage a complicated lie. It tends to get more complicated as it goes on, as the con artist needs to refine it and add to it constantly. Every modification has the potential to cause a conflict that someone will notice, and upset the apple cart.
The con artist bears no remorse for pulling off the scam, no matter who might get hurt, or how badly. They regard the victimization of others as their mission in life, and even rationalize it by claiming to have educated their victim to be more wary in the future. If the victim leaves themselves open to the con artist, it is the artist's duty to exploit them. They think of this as their job.
The pathological liar only wishes to improve his own image with others, and in severe cases, himself. If people are victimized as a result of his lies (which isn't uncommon), the victimization is unintentional. Their immediate goal is to be better than you, and ultimately to be better than everyone. They will have a "topper" story for every one you tell. If you have a house worth $200K, they have one that cost $400K, and a summer home at Lake Tahoe. If you had two eggs for breakfast, they had three, plus waffles. They aren't especially skilled at managing the lies, and often tell them without thinking through how they will support the back story. They'll claim to have won the Medal of Honor in Vietnam, even though they were in grade school when hostilities ended there.
The "pathological" part comes when the liar starts to believe their own legend. This begins when they revise actual memories and history to improve their role at the time, but after they've told the story often and long enough, they believe it themselves. If they're called on it, they'll become defensive and even violent. They have a huge fear of being revealed, because that usually means the whole house of cards they've built will fall soon thereafter.
There are con artists in law enforcement, and they tend to excel at working undercover. This is one of the few times the con artist's skills can be put to good works, since the people being victimized are usually crooks. I knew one of these types in graduate school. He was a narcotics detective for a sheriff's office in Florida. His skill as a con artist was first revealed while watching him seduce women in bars, for a goal of a very short-term, unmeaningful (at least, as far as he was concerned) relationship. He concocted a different story for every woman I saw him meet, and played each role perfectly.
One night, he told me in advance he was going to do this, and that I was going to be part of his legend. We had come from a reception given at a faculty member's home, and had stopped at a club before going back to school. There were seven in our party, all cops except one. At the moment, I was the only one wearing a coat and tie. Two women came into the bar, and he immediately introduced himself as a real estate developer from Birmingham (we were in Tuscaloosa, Alabama at the time--Birmingham is about 70 miles away, and the largest city in that region). He was in town to negotiate financing for a condominium development he was building. He introduced me as "Tim O'Hara," his accountant. "See how serious he is, coat and tie and all that s***? All he does is worry about my money. I love this guy." Other aliases were supplied for the others in our party. I wouldn't have even been able to keep the names straight. I left the party before I could see how far he was going to take the scam, but I can guess how it turned out. He had a very good track record of success with the ladies, although they might have characterized the experience differently.
The con artist seems too good to be true. He arrives just when you need someone with his skills or resources, as if sent by providence. Nothing about him will cause you to be suspicious or will put you off. He will have tremendous, almost psychic insight into your needs and situation. By the time you give him access to the things he needs to exploit you, he will have your complete trust.
The pathological liar is equally convincing on his face, but his accomplishments never complement your own--they will always exceed them, and those of anyone else around you. If they've ever done anything wrong, they will characterize it in such a way that you will feel sympathy for them. They have a compulsion to be loved, respected, and accepted. When pressed for details about their CV, they will either be evasive ("That was all classified, I can't talk about that") of the supporting facts will be something even more fantastic than the base story.
If revealed, the con artist will try to laugh off his scam, or just look for a quick exit. The pathological liar will become intensely defensive. The con artist knows that his deception will eventually be found out, but he hopes to be away and clear before that happens. The pathological liar really believes (or wants to believe) that he's pulling this off and you'll go to your grave thinking of him the way he characterized himself. By the way, I've used the male pronoun throughout this response, but I've met just as many female con artists and pathological liars.
As I said, this is all based on my personal experience and perceptions. Someone with a better and more formal understanding of psychology can provide you with something more definitive.
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