A criminal prosecutor says this is the No. 1 sign you're talking to a phony

Sometimes you don't know you're dealing with a phony until the damage is done.

That's why Wendy Patrick, deputy district attorney and team leader in the Sex Crimes and Human Trafficking Division for San Diego, who is a frequent contributor to CNN and FOX, wrote the book "Red Flags."

She wants to help people spot a phony - someone who is insincere or deceitful - before it's too late.

"I read red flags for a living - around the clock," she writes.

Over her 20 years of detecting and prosecuting criminals, Patrick told Business Insider she had picked up on one telltale sign you're dealing with a phony: it's called counterintuition, or "when the optics don't match the topics."

When a person's eyes, smile, and cadence all line up during a conversation, we tend to trust the person on instinct, she says. But when someone speaks to you and the person's actions don't match what he or she is saying, you may get an uneasy feeling because your counterintuition is kicking in to alert you that this person might be a phony.

"Even with the most polished speakers, a verbal-visual mismatch triggers distrust," she says.

A common example, Patrick says, is when a beautiful, smiling newscaster is reporting the details of a horrible tragedy. Her words don't match her demeanor, and it makes us uneasy. "It's because instinctively we recognize that it doesn't fit."

One exception is polished manipulators, she warns, because they are sociopaths and don't have a conscience - meaning they can easily cover up their true intentions. "They don't have the kind of moral net that would enable them to behave according to societal norms," she says.

But excluding chronic manipulators, Patrick says people can help protect themselves from phonies by making sure their mannerisms match their message. "Trust your gut feeling when what they're talking about doesn't match their demeanor."