Former FBI special agent Dr. Jack Schafer, who specialises in behavioural analysis, said there are three signs that one can use to detect if a person is lying.

"I want to believe salespeople when they say the product they are selling really does what they say it can do. But sometimes I suspect some of the people I deal with are not being completely honest," Schafer writes in The Muse.

He said confronting people about a lie "is often awkward because of the sensitive nature of our relationships."

"The challenge is to identify disingenuous behaviors without damaging relationships," he said, adding that he compiled several techniques in his book "The Like Switch" to know deception without being detected.

One technique he calls is the "Land of Is."

"Yes or no questions deserve a yes or no answer. When people cannot or do not want to answer yes or no, they typically go to the Land of Is," Schafer said.

This was derived from former U.S. President Bill Clinton's statement, "It depends upon what the meaning of the word 'is' is. If 'is' means is and never has been, that's one thing. If it means there is none, that was a completely true statement."

Schafer said the concept "occupies the space between truth and deception."

"The Land of Is consists of half-truths, innuendos, suppositions, assumptions, and verbal judo. Most people want to tell the truth, so they go to great lengths to contort the English language to maintain the illusion of truth without telling it entirely," he said.

To test it, ask people a yes or no question. If they cannot answer yes or no, it's a sign that they are lying.

Another technique involves the word "well."

Schafer explains that "if you ask someone a direct yes or no question, and the response you get begins with the word 'Well,' there is a high probability of deception."

"When a person answering a direct question begins with 'Well,' it indicates that he or she is about to give an answer that he or she knows the questioner is not expecting," he said.

The third one is the "why should I believe you" concept.

"When truthful people are asked why others should believe them, they typically answer, 'Because I'm telling the truth' or some variation thereof," he said.

Schafer said people who lie find it hard to say "because I'm telling the truth" because they are not telling the truth and they use responses such as "I'm an honest person," "You don't have to believe me if you don't want to," or "I have no reason to lie."

Schafer cautioned though that the methods do not detect lying completely.

"If a person answers questions directly, you can have confidence that the answer is truthful and that the person will not be aware that you have tested their veracity, thus preserving the integrity of ongoing relationships," he said. "If the person does not directly answer questions, it does not necessarily mean you are being deceived, but you should examine the person's answers in greater detail."