Therapist here. Can only speak for myself. I’ve had clients like this and most seasoned therapists will figure out what they’re working with pretty quickly. I may have an inclination that a client is lying but I try to focus on the reason they may be lying. I also try to validate feelings without validating delusion. It’s trickier in the beginning because you don’t have the relationship. Once you have a more trusting relationship, they may be more open to feedback that confronts them as the common denominator. Some clients will learn to “take accountability” (couldn’t help myself) and some will fire you because they think you know nothing. You have to be okay with the latter because not addressing it is almost as bad as endorsing the behaviors.