If you are aware of how to negotiate, why would you stop negotiations,
just
because someone was using NADA prices as part of his negotiations.

**************

If the gap is hopeless, refusing to "counter" can be an effective
tactic. (If the gap is hopeless)

It has everything to do with carving out the game rules.
Is the question going to be, "How much more than half price will you be
able to eventually grind out of me as a buyer/" or "How much less than
my asking price are you going to convince me, as a seller, to accept?"
The answer is seldom "double", or "half".

A fair price is what a willing buyer will pay a willing seller. Anybody
will be willing to buy at half price, but few willing sellers, (not
acting under duress) will accept that.

Those who need to buy on the triple cheap should maybe keep an eye on
the obits. Next time a boater dies, maybe his grieving widow can be
deceived into dumping his boat for a lot less than it's really worth.
Once in a while you meet a guy who bought a boat, a car, or something
else on the super-cheap in such circumstances.......don't know about
you, but I have to resist the urge to vomit when they start bragging
about how they suckered the old lady in her hour of distress.