Did the robots, which have less than 100% honesty settings, ever lie in such a way that the audience and/or characters may have been tricked? This plot point seemed important when addressed directly during the story, but I missed if it ever opened up the door to a classic Nolan teaser, where what we think is true may not be true. Thoughts?
No, not really.
CASE had kept his disabling of the craft's docking ability to himself, out of suspicion of Dr. Mann, but that's it.
For some time I thought the reveal that
Plan A was a lie
would cause the robots to start fighting against the human astronauts, HAL-style, but this never happened.
Consider when Romilly asks Cooper for another chance at Gargantua, TARS is brought up as the candidate to glimpse the singularity; Cooper asks TARS if he would be willing to do it for them.
TARS: ~"Before you get all teary-eyed, remember, as a robot, I have to do anything you say."
Cooper: ~"Your cue light is blinking" (It is not as I recall).
TARS: ~"I'm not joking." (The cue light comes on with this statement).
It would seem this generates some ambiguity, especially considering that Cooper recycles these same words to justify to Brand as to why TARS will get ejected into Gargantua. This might be Cooper joking, but it isn't dismissed. TARS replies again ambiguously
this is what we always planned.
So either TARS is an altruistic robot capable of self-sacrifice, or, TARS is fundamentally under human control, just accidentally altruistic. The film seems to sell robots as being under the control of humans, but the film also builds TARS as a dynamic character and key to the film's most emotional scenes...perhaps the first exchange is TARS using his poker face (it seems clear the robots learn), integrating his humor setting and his honesty setting.
Anyway, I'd say that's some trickery used on the audience/characters.