When you're being interviewed for a job always ask “what happened to the last person?”
It's a great way to catch the interviewer off guard because a) they rarely expect challenging questions and b) least of all this one.
Meaning, it's not usually a question they'll have a rehearsed answer for. Which usually means, you'll be able to easily interpret the answer. You'll be able to interpret how long it takes them to answer, what they say in their answer and how they answer.
Length of time to answer: a good employer should know straight away and not be searching for a palatable reason.
What they say: this one is obvious, but can be subtle such as “why do you ask”. This typically shows that they don't quite understand why previous employee relationships or turnover are important factors
How they say it: because you've asked them a question they typically aren't expecting, you'll get a more subconsciously manifested way of saying something.
It's not foolproof, it won't apply to every job, but it is damn effective. It's helped me turn down several jobs. And sometimes it's exposed the most stupid of bosses who will outright rant about the previous person (in those situations act sympathetic to get them to truly show their real side). I've had it where an interviewer has gone from a bed of roses to a bed of thorns with just one question.
(Another good question that's related to this one, and applies for practically all jobs is to ask what the employee turnover rate is)
((I appreciate that this tip may not apply to everyone and that some people will be in the difficult situation where they have no choice financially but to just take what they can get. To those people I feel your pain, I've been there before.))