Honestly, the only place where you can currently get genuine company reviews today is Blind, if you can stomach the trolling. The so-called 'kool-aid drinkers' or 'hr puppets' are called out (often humorously) all the time.
For Glassdoor, I am not surprised, this is not news. I interviewed at an awful company once which had stellar - I mean actually straight-A's 'nothing wrong here, we're the best, if God came down from heaven and founded a company, this would be it' reviews. Found out from an ex-employee after they've been acquired by the company I worked at that they were pestered daily to write positive reviews.
The rule is to not trust any online entity ever. That's just common sense. So everything you write online anonymously should be filtered by the 'What would I feel if this text will appear next to my name and my company name in the New York Times tomorrow morning' filter.
For Glassdoor, I am not surprised, this is not news. I interviewed at an awful company once which had stellar - I mean actually straight-A's 'nothing wrong here, we're the best, if God came down from heaven and founded a company, this would be it' reviews. Found out from an ex-employee after they've been acquired by the company I worked at that they were pestered daily to write positive reviews.