Glassdoor operates as a sort of extorsion to businesses. It provides a place for disgruntled employees to vent, and vent they do. It doesn't matter how much truth is in the posts; Glassdoor will stand behind it because ultimately, they want you to pay them to "clean it up," and most do. Companies try to compete with it by offering "incentives" or pushing employees to post positive things. The whole thing is ridiculous.

I think Glassdoor's concept is excellent, but the business model ensures employees or employees can't trust it.