When you submit a review on Glassdoor, they must review and approve it before it is publicly available. About a week ago, I posted my negative review of GM and the post was approved. Oddly, it would not show when sorting by "Most Recent". I could only get to it by going to "My Profile >My Contributions > My Reviews".
I then made a simple whitespace edit in order to make it more readable, this triggered another review on my post. This reviewer was apparently triggered by my review and removed it from Glassdoor with no explanation. Seems the review process has a fair amount of subjectivity in it.
I'm in the process of contacting them. I plan to repost the review after I find out exactly why it was removed.
The anonymous company reviews are the single most useful part of Glassdoor as it often gives insight that you won't receive from anyone else - least of all, recruiters. It appears that Glassdoor's integrity could be compromised by a rogue reviewer with a hidden agenda.
I'll come back to update after I have a chat with them.