'Pathological liar' is absolutely the toughest individual to deal with as a psychiatrist. Because you can't take anything they say at face value. And you can't, you know, fill in their personality. You don't know what's real and what's not.
A psychologist evaluates, diagnoses, treats, and studies behavior and mental processes.Some psychologists, such as clinical and counseling psychologists, provide mental health care, and some psychologists, such as social or organizational psychologists conduct research and provide consultation services.