I agree with stopdog - I think most therapists lie.

I truly believe in many cases they do it because the truth takes too long to explain, would unnecessarily derail the session or cause the client excessive distress.

I would take issue with certain types of lies, i.e.:

"I'm out next week and can't see you." But find out they are actually working.

or

"I really like working with you!" But find out they dread my appointments.

The little things, I would assume they just don't want to put in the effort explaining.

But that's just me.