There is no ultimate solution to this problem. In each instance one uses one’s best judgment. But it pays to be aware of this set of choices and of the way the exercise by one party of choices to follow a competitive or cooperative strategy can itself be transformative for all parties.
Nothing can destroy trust and good will like the discovery that one has been lying or that one is operating with less than candor. Counterparties will clam up and be more inclined to resort to competitive approaches in self-defense if they perceive a negotiator to be dishonest or insincere. Crafty conduct can not only hurt one in the instant negotiation but also can wreak havoc on one’s reputation in the long run.