However, I can't find anything official about either and Wikipedia isn't very helpful. They do have some information about their existing funding:
https://en.m.wikipedia.org/wiki/Glassdoor
A part of me thinks this type of thing would make a good not-for-profit enterprise. I'd even consider some sort of government backing. I'd say a service like that has good social potentials and can help society to make nformed choices.
So yes, Glassdoor's intensive structure is aligned to make employers happy. They don't take any income from individual review contributors or readers.
However, it seems that their business model is then catered, at this time, to employers and they have made themselves a niche area in the reputation management sector. Though not alarming at this time, I can see this going south quickly and without warning (Equihax for example)
I ask, as the payment method is critical to understand it's reliability.
If it is ads, then yes, I think it should be reliable. 'You' are the 'product' in that case. More negative press will likely keep you clicking and searching about, therefore more money.
If it is the companies, then it it not likely reliable. Why would you pay a company to essentially bad-mouth you? You pay them for good press (the pizzeria in NY on Yelp being an egregious exception). I'd say this holds if the companies can pay in any way at all. If they can influence for dollar, even rarely, then the whole thing is suspect.
Anyone know the real answer?