I apply the same metric I apply to online product or service reviews. If they appear on a regular cycle, or if they appear in some of there kind of statistically improbable clumps, or if there are no negative comments at all, then they may not be entirely plausible.
Employment verification won't help on Glassdoor, because it would be the easiest thing in the world to hint to a group of the most settled employees that maybe they could leave positive ratings.
It would help against malicious negative reviews - which can also be a thing.
Websites with reviews are doing a disservice to users by not giving us tabulated reviews and tools to view detailed statistics. I'm reminded of 538's impressive interactive data exploration pages.
Employment verification won't help on Glassdoor, because it would be the easiest thing in the world to hint to a group of the most settled employees that maybe they could leave positive ratings.
It would help against malicious negative reviews - which can also be a thing.