No matter the business, no matter the job, everybody who works for a living has this much in common: Somebody is going to tell them a lie. If not every day, then certainly every week. And if not an overt display, a covert display.

Figuring out how to tell when an account executive or anybody else is stretching the truth — or telling an outright lie — can be a big challenge.

"I think all of us have the capability," said Gregory Hartley, who co-wrote the recently published book "How to Spot a Liar: Why People Don't Tell the Truth and How You Can Catch Them."

"The difference between the average person and a trained interrogator is a set of extreme interpersonal skills. Instinctively, we all know how to do it," Hartley said.

The military interrogator has worked with or for the Army, the Defense Intelligence Agency and the Navy. He believes there are three varieties of lie: commission, omission and exaggeration.

His advice for finding untruths in person-to-person encounters with, say, an account executive trying to sell something, is simple enough.

Chitchat first to develop an impression of the person in an unstressful setting. Unthreatening small talk will offer a glimpse of what Hartley describes as baseline impression. Note body language and posture.

Then, as the topic moves toward business and the account executive's pitch, ask a few probing questions. Be particularly concerned when hands start to fly and feet get busy.

Any altered behavior might signal an exaggeration at best, a lie at worst.

"Anytime you see a change in demeanor, say, they are normally quick and now react slow or they are slow and react quick, that is a big indicator," Hartley said.

Telephone encounters are tougher, but it is not impossible to detect a lie.

Again, Hartley said, generate a mental, baseline model of behavior for the person during the early part of the conversation.

As the topic moves from social to business, note what is being said whenever there is any kind of deviation — a change in cadence, vocabulary, volume or tone of voice.

The changes suggest stress, and stress can imply a lie.

Sheri Johnson, a teacher for 13 years and a principal for six in the North College Hill City School District in Ohio, is something of an expert on untruths as well. Her students, however, are often a lot easier to decipher than a salesperson with 20 years of experience when it comes to fingering a lie.

"Usually, they have trouble making eye contact," she said. "And their story changes.

"When we have some incident, I usually start out by telling how important it is to tell the truth and point out how it makes you feel bad inside when you are not being honest.

"Usually they'll agree, and often that's all it takes."

Hartley has another reminder for any would-be interrogator: People have trouble not communicating their true intent.

"Often," he said, "we forget that we are animals first and humans second."