To spot a liar, particularly during negotiations, pay attention to someone saying "yes" and then later saying "no."
"Maybe the party was lying to you, or maybe they were just engaged in wishful thinking," Voss writes. Regardless, use the "Rule of Three" to make sure the "yes" you hear is a solid "yes."
"The Rule of Three is simply getting the other guy to agree to the same thing three times in the same conversation," he explains, since "it's really hard to repeatedly lie or fake conviction."
To avoid sounding like a broken record when using this strategy, you can vary your tactics. Says Voss: "The first time they agree to something or give you a commitment, that's No. 1. For No. 2 you might label or summarize what they said so they answer, 'That's right.' And No. 3 could be a calibrated 'How' or 'What' question about implementation that asks them to explain what will constitute success."
Alternatively, you can simply phrase the same question in three different ways over the course of the conversation. For example: "What's the biggest challenge you faced? What are we up against here? What do you see as being the most difficult thing to get around?"