Glassdoor is a phenomenal resource.

For one thing, it's leveled the playing field for  job seekers. By giving ex-employees the chance to write honest--and sometimes unflattering--reviews about their previous employers, Glassdoor has helped people identify bad companies and  toxic cultures before signing a contract.

But Glassdoor isn't just for job seekers. Many others use it at a more enterprise level--to research potential clients, for example. A few months back, my team and I decided not to work with a company after reading some troubling reports about its culture on Glassdoor.

Glassdoor and similar company review sites have become so important that sustained negative reviews can be a major barrier to both recruiting and partnerships. As a result, many companies actively try to cover up bad reviews and mislead job seekers.

Posting some fake positives probably seems easier to many than addressing substantive issues. But a company that is actively trying to cover up its issues is always a worse bet--both for job seekers and potential partners--than one that's comfortable with its own image.

Over the years, I have worked with hundreds of companies as a client, partner, customer or employee. In that time, I've learned to spot the signs that a company is misrepresenting its values or its culture online. Here's how.

Know what a coverup looks like.

Every company has current or past employees who are unhappy in some way; it's unavoidable. That means every Glassdoor page will likely have some bad reviews. However, if the reviews you are reading sound as if they were written by Jekyll and Hyde, that's a sign of a company that's putting more effort into misleading people than it is into addressing its core issues.

If you find a Glassdoor page with a long pattern of detailed negative reviews followed by a spike in shallow positive reviews, that's a red flag. You may notice the positives were all written on the same day or in quick succession. In such cases, chances are high that the glowing reviews were written by management or people pressured to try to put lipstick on the pig. Subsequent reviews may even point them out as false.

If you think a company that interests you is posting fake reviews, check out the "Rating Trends" graph on Glassdoor. This tool can help you to identify a spike in positive reviews that doesn't look consistent or genuine. The long-term trend is the one that matters.

Don't be conned by "cons."

You can learn a lot about a company from the nature of the "cons" sections of its reviews. Fake or manufactured reviews often include cons that seem trite or unrealistic. Examples include: "People are too nice," "People don't appreciate how great it is to work here," "N/A," "Can't think of any," or, "There are zero cons here."

Ideally, cons should identify specific areas for improvement. If the negatives are big things--the CEO is a micromanager; the culture is unsupportive, etc.--that's a bad sign. It's possible to work with a company where the negatives are small things that can be improved, such as inadequate benefits, or insufficient training. Poor leadership and culture emanates from the top and is unlikely to change anytime soon.

You should also be very wary of any companies where the reviews describe leadership or the company culture as "toxic" or where the word "beware" pops up again and again. I can't think of another word that carries as much weight in a Glassdoor review. When "beware" is used to describe management, run!

Be skeptical of "pros" that are just perks.

Pay close attention to the pros as well. They should be substantive, not a matter of window dressing. For example, if the only pros reviewers can come up with are things like "free food," "a cool office" or a "casual dress code"--that's not a good sign. Nobody comes to work for the snacks. At many unpleasant workplaces, such perks are used to distract from poor leadership and culture.

The pros should be about people, processes and the company's product. Great leaders and supportive teammates doing good work together are fundamental to great company culture.

Even more important than a high rating is authenticity. While you probably don't want to work for a company with a bad culture, you definitely don't want to work for a company that's dishonest. The good news is, thanks to Glassdoor and other review sites, these companies are increasingly easy to spot and avoid.