How much should I trust Glassdoor?

Im a little worried about a potential job opportunity, they have really bad glassdoor reviews 2.6 and its a major megacorp. Three of my coworkers have defected to this company and they all considered great experts in their field with a strong good work ethic. My relationship with them is also great but they dont work in the area where I will be so they wont really know the ins and outs, also we all get along great but not to the point that i could call and ask them anything about this company, (they are all “head of xxx”) . I know they left their old jobs because of pay etc but i don’t know if they are miserable at this megacorp or not.

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