Let's just say that I have spent my entire adult life, in close relationships with some of the most untrustworthy S.O.B.s on earth, and have learned to deal with it.
Many folks think, because I am friendly, open, and kind, that I'm weak, naive, and gullible.
They tend to get quite upset, when they find out, that's not the case.
My point is that these lying assholes are not doing something "harmless".
I realize that most folks don't have four decades' worth of experience, dealing with hardened criminals, con artists, and generally delusional people, to firm up their personal boundaries.
I've found that a good start, is not to do things like apply emotionally-charged labels to the folks doing this. If they are dangerous, or present a risk, they may be sanctioned, imprisoned, whatever.
But I have found, in my experience, that offering kindness, where none is expected, is often key to helping folks turn things around.
As I said, many of these people are living in their own personal hell, where they hate themselves, and the world around them, and that tends to set up a reinforcement feedback loop.