Its not really in their interest to answer dishonestly: if I take the job and it turns out the work/life balance sucks, I'll leave, and they'll have wasted a lot of time & effort on me.

Also, the people I'm asking are typically engineers, they're not inclined to lie about things like this, and they're not expert spin doctors. Plus, when I go for the full day interview and talk to many people, I'll ask many of them about it.