What are some examples of "hard questions" that we can ask?
If they have good answers to those questions that don't feel like canned responses, then go dig deeper. Ask their employees about their leadership style - do the answers match? Does their resume and google-stalking match their story of their history? Ask the team about organizational conflict resolution. You should get similar responses.
Also, think about whether they talked to you like a leader. I've had interviews when I really enjoyed talking to the potential boss, and it felt friendly, and those turned out to be sub-optimal leaders. But the good leaders I've worked for interviewed in a way where I was comfortable, but challenged by the questions, and they stayed focused. They didn't chit-chat or make friends (at least not beyond just a few quick minutes as we got started), they drove towards getting the answers they needed to see if I was right for the job, and they gave me opportunities to ask questions back.
In the startup world, bullshitters are pretty much the norm, so finding bullshit isn't difficult. What's difficult is ignoring the hype bubble and social pressures that come with challenging people who are well-funded (and of course, sometimes you're wrong, which is part of what makes it hard).
Even if you're wrong, though, a non-bullshit answer to a pointed question will address the question. Most people, however, will just say words that dance around your question, clarifying nothing. In that case, you have to have the guts to keep asking followup questions, even if it makes the bullshitter uncomfortable.
When I think back over my history, I've always had a pretty good idea about the bullshit level of various employers simply by asking simple things like "how do you make money?" Good entrepreneurs will simply tell you (even if the answer is "we don't, yet"). Bad entrepreneurs will dress it up and try to hide their answer in word salad. Avoid these people.