What are they afraid of?

If you can help Christians answer this question for themselves, for their own lives and their own ministry involvement, you help them take a big step towards maturity as they face fear with the god who provides and promises to look after them, even while their worst fears come true before their eyes.
I reckon this is the big question to get people to answer for themselves as they approach thinking about doing MTS and a life of full-time ministry. If they can identify their deepest fears about giving their life to the work of the gospel, it might not make the decision easier, but it will afford them the chance to grow in their love and dependence on God.
Don’t ask it straight off the bat… You gotta work to get that deep.

Address people’s emotions before you address their questions

If someone asks you a difficult question, or a personal question, or an emotionally charged question, chances are they’re not going to be listening to what you say.

Instead, all that’s going to be going through their mind is… How will he deal with my feelings? How will he feel about me after I ask this question?

By asking a question, they’re really putting themselves out there. So don’t leave them hanging. Reflect their emotions back to them. State the feelings behind the question. E.g. “I can imagine that could have taken a lot of courage to ask that. Thank you.”

Only after you’ve dealt with their feelings and fears have you then got the opportunity to answer their question.