I like the concept of Glassdoor as it enables employees to confidentially write employer reviews, therefore generating insider knowledge for those considering that employer as their next career move. The risk with anything TripAdvisor-esque is that it can be manipulated and of course is one way traffic. Therefore an employee sacked for gross misconduct could write a very negative review which is reasonable to assume is unjustified. Yet an independent reader wouldn't know the background.
Likewise, a business may pressure its employees to write positive reviews and monitor what they input. Finally we spend a lot of time flagging reviews that are about Aspire, good and bad, but nothing to do with us. They are different employers of the same name, my favourite being a dentist in the US. The reviewer felt proud to work for Aspire "as most people left able to smile widely and brightly with super white teeth". It was tempting to leave it as a review.
...it is highly unlikely that fake reviews make it onto the site. “We require each person to certify their employee relationship to the company when they post any content"