The Biggest Red Flag in Job Interviews

Let's not kid ourselves: What we see in a job interview is rarely what we get. Everyone is on their best behavior—both the hiring manager who's talking up the company, and the candidate who's trying so hard to be liked.

And unless you've been trained by the FBI or the CIA, you're never going to get the truth out of anyone within just an hour. Everyone talks about "authenticity" these days, but too many people don't understand what it really means, mostly because they're too busy trying to be what they think the other person wants.

Every hiring manager I've worked with has agreed that "phoniness" is their worst nightmare. Once this trait is spotted, a loud "DO NOT HIRE" alarm goes off. Your goal, as the job candidate, is to provide a true sense of who you are, what you stand for and how well you'd fit in. Given the high stakes and costs — in dollars, morale and lost opportunities — of a bad hire, phoniness is the ultimate opportunity killer.

If you really want the job, don't try so hard for likability that you come across as dishonest, especially in those crucial first seven seconds of an interview when you make a first impression.

Here are some of the most common pitfalls to avoid:

1. Shiny car syndrome

There's a reason why car dealers wash every car on the lot on weekend mornings. Whether it's a Rolls Royce or a Chevy Volt, shiny attracts the eye. But the "shiny" candidate with the never-fading smile comes across as vapid.

Avoid overdoing it with the obvious actions that radiate phoniness, such as nodding "yes, yes, yes" or "I agree...good point…I was thinking the same thing." It's also easy for hiring managers to spot false laughter, like the canned soundtrack from 1970s sitcom.

2. Lies, deceit and other games

If you fabricate and exaggerate on your resume or in an interview, it's game over. Hiring managers check where you've been and what you've done. But those aren't the only lies. It's shocking how many candidates come across as eager to engage in the interview process with assignments and follow-ups, and then never do them.

(I recently met with a candidate who made a great first impression. However, before the interview, his true colors showed. He repeatedly said he'd already taken an assessment (not true) then promised he would (never did). His lack of honesty and follow-through made me question everything he said in our meeting—and he was out.)

3. Mr. or Ms. Teflon

Nothing sticks to this person, neither an opinion nor an impression. Instead, the Mr. or Ms. Teflon intentionally slides along by agreeing with whatever has already been said without an opinion of their own.

One of two things is going on here: They haven't done their homework and can't say anything substantive, or they're so insincere that they duck any opportunity to share a contrary opinion. Most interviewers like the give-and-take of diverse opinions that make for an engaging discussion. Instead, at the end of the interview, Mr. or Ms. Teflon slip-slides away without leaving any trace of an impression, opinion or who they really are.

4. The name dropper who knows no one

This happens all the time. In trying to prove how well connected they are, name droppers make it sound like they know anyone and everyone a hiring manager mentions. There is not one person, company or organization that the name dropper doesn't know and doesn't "love" (e.g., "Just saw her last week...great person," "Close friend — I'd do anything for him," "It's been a good two years, but absolutely we're close," "I remember when" or "Let me tell you a story."). It only takes one—maybe two—phone calls to reveal a name dropper.

Master your EQ

You can avoid these common pitfalls with a good bit of emotional intelligence. Being more self-aware and attentive to the person in front of you can help you better present your most authentic self. Here are a few ways to do it:

• Leave your Instagram self at home. Your interviewer wants to see the real you, not the glossy, made-up, Instagram-vacation-photo version of you. This goes beyond being well-groomed and dressed appropriately. Your verbal and nonverbal communication needs to convey your passion and purpose, what you care about and why. Do your best to forge a real connection.
• So, what do you think? If the interviewer asks for your opinion, speak honestly. For example, the hiring manager describes a scenario and asks what you would do. If you've done your homework about the company's products, biggest markets and strategy (earnings calls, press releases, and annual reports are a goldmine for research), you should have an informed opinion. The hiring manager probably isn't looking for the right answer, they simply want to explore what you know and how you think.
• Be refreshingly honest. You'll have to get a read on the interview atmosphere for this one, but if the hiring manager seems to be a straight-shooter, then candor is your best policy. (One of the most refreshing interactions I've had recently was when I asked a candidate his opinion of someone we both knew. The candidate looked me in the eye and said, "The only time he's lying is when his lips are moving." I was shocked (pleasantly) at the candor, but his comment was so spot-on accurate, it made a real impact. Risky? Yes, but it worked.)

With everyone trying to be on their best behavior, interviews can be artificial enough. Don't make it worse by being phony. Otherwise, you might as well have the entire interview staged with a makeshift set and lighting.

For more career advice, consider Lose the Resume, Land the Job or Korn Ferry Advance.

A version of this article appears on CNBC.com.