Comment by Peroni

Glassdoor isn't gospel but it is a useful data point.

>How do you realistically tell from outside if a company does treat their people well, or has a difficult culture?

The challenge there is that everyone has different interpretations of 'a difficult culture'. What's important (albeit difficult) is establishing an understanding of the type of environment you thrive in and the types of environments you struggle in. With that understanding, it's important to spend time during an interview process asking open-ended questions that might reveal the aspects you love/hate.