Here's my strategy: Read the glassdoor reviews - If it mentions "people crying at their desks", that's a bad sign - actually any kind of crying in a professional environment is a bad sign. Also, words like "high energy" and "passion" often reflect poorly as well.
#2) Ask the company about their employee retention rate or research it online. If you can get an accurate picture of their retention rate, then you can find out how toxic it is. The greater the number of people leaving, the worse the place is.