There is more than one way to be honest about a situation. This person can start talking about the company spitefully, trashing them to the interviewer. Unfortunately, some folks that do this also do the same to their current employer or coworkers.
Now, I don't know about you, but I'd rather not knowingly hire in this sort of toxicity. Tough love and unfiltered opinions (honesty) can simply be an excuse for being an asshole when there are other options.
The person can calmly describe that there were pre-existing problems, though, hint and be honest at them (but not dwell), and go on about how they learned some life lessons and so on. When describing the issues, use fairly neutral, non-value-based terms.
So instead of saying, "The company is shit", you can say things like, "I'm not happy at the company" or "I don't feel like i*m a good fit for the culture there". Perhaps your honesty needs help with presentation.