As a seasoned podcast host, I've conducted hundreds of interviews and have established rules for my guests.
My top rule? Conducting pre-interviews with upcoming guests, which are crucial in producing quality episodes.
I'm in charge of the interview, but depending on the guest (and topic), will sometimes check beforehand if they're comfortable discussing potentially sensitive topics. If you have a reputation for being fair to guests, you probably won't get a lot of pushback, especially when showing this kind of concern to treat a guest (and the topic) with care.
My main rule of engagement is: feel free to decline answering any question that I ask.
While I aim to respect personal boundaries and avoid embarrassing moments or "gotcha" situations for guests, the listeners' needs always come first.
I don't mind if a guest doesn't want to answer a specific question or talk about most topics. However, repeatedly avoiding questions may lead to the interview not being used as it could affect listener satisfaction.
Guests are not interchangeable and you bring a guest in for a specific reason. There's no point in sitting down for an interview with somebody who doesn't want to talk about what the audience is interested in.