It's definitely easier to spot the soul sucking companies. They are the ones with the majority of bad reviews spotted with glorious reviews left by management trying to up their average.
I usually don't post reviews, good or bad, on Glassdoor, because I can just imagine the fallout of a data breech/hack which would end up doxing a ton of old disgruntled employees.
I don't think Glassdoor has very stringent identity checks (a problem in itself), so I imagine most posters are using throwaway email accounts to shield themselves from any fallout.