Yes, clients do sometimes lie in therapy, and I’ve had my share. Here are a few examples I remember:
An alcoholic says she stopped using when she hadn’t. I had no way of knowing except by hunch, and you can’t confront someone for lying because of a hunch; it could be very disrespectful if you are wrong. By the time the spouse was able to see the lies, the alcoholic client in this case left treatment with me.
An unfaithful partner tells me and his wife he has ended an affair when he hadn’t. The truth came out eventually and I was able to say how it felt to me, and how much time and effort I had wasted, because of the lies.
A Narcissistic Personality Disordered person told me how useful I was being to him so he could tell his wife he had “been to therapy” and in hopes of keeping me from confronting him. It didn’t work, because this one I could see through.
I’m not very patient with devious people who waste my time. I usually ask them to leave, or offer a “one more chance” proposition when I think fear is the dominating motivation rather than straight up manipulation to avoid growing.