Make the other comfortable.
There will probably be some topics that are not so comfortable to talk about. It is your role to try to make the other as comfortable as possible to share whatever it is that they need to share so you can determine if this they are a good match for you.
You can start by allowing them to share at their pace. “I Know that this is tough, we can do it in small bits if that is more comfortable for you.”
You should also let them know that you will not pry. “It is important that we discuss [X]. It is your story, so if I ask questions that not relevant, don’t feel compelled to answer.”
You can build trust by explicitly telling them that you know that it is their story and that you would never share it.