NNTD as a framework mostly takes for granted that people are trying to tell the truth; if not, you have a different kind of problem
that's not to say that it's vulnerable to people lying, just that it doesn't have anything in particular in its toolkit for navigating such a situation
NNTD suggests backing out to the point where you can get common-ground, and if someone is regularly lying or bullshitting it's going to be very hard to find common-ground of any kind, so you might end up just backing pretty far out of the relationship
the main thing that NNTD would say is that if you find yourself in a situation where you can't trust that someone isn't flat-out lying to you
then step one is to honor internally that you're having that perception
and if the situation affords it, you might reveal that you have that distrust
and if the situation doesn't afford that space or can't respect that you have that distrust, then probably you want to get out if you can