So – does the other side really mean what they are saying? 

Will they  really do what they are promising to do? I’m pretty sure that you and I  can’t tell. The reason that we are so bad at detecting deception is because the most common signs of deception, such grammatical errors  and as increased blinking, tend to be quite difficult to notice and  interpret correctly. In addition, it may be difficult or impossible to  determine whether the other side’s claim is true or not. 

If we can’t  count on being able to detect lies, a more fruitful approach may be to  find ways to discourage the other side from engaging in deceptive tactics in negotiation in the first place.