Polygraphers who give probable-lie control question tests believe that it is ethical to lie to their examinees about the purpose of the control questions, presumably because they believe this will aid them in their quest to clear the innocent and catch the guilty.
Do the polygraphers who give these tests believe that it is also ethical for the innoncent examinee to lie about his/her use of countermeasures since such a lie will also make it easier for the polygrapher to correctly decide on his/her innocence?
The end never justifies the means, ever ever ever. Any polygrapher worth his salt is thus without ethics, for they know their profession is based upon lies and deceit on -their- part. If they feel that a few lies catch more guilty parties than not, then they are doubly guilty. They have the temerity both to feel that it is okay to lie AND that they can read a chart and determine if you're lying or not.
If they really want the whole truth, then they should give you the whole truth. They should give everyone a copy of TLBTLD to read a week before the exam, so that when they begin their pro schpiel, you can know the con side.
Systems of any kind based on lies are tyrannical by definition, and...
"An oath to a tyrant is no oath at all."- "Braveheart"
So I see no ethical quandary in conning the con man...