Just ask some necessary questions but very important.

first you have to ask their names. age.
how was their business?
what kind of business do they have?
what is in their mind, why they choose that kind of business?
it is inherited or not?
give some advice how to run that kind of business smoothly?
what kind of strategies they applying on their business.?

(it is enough to conduct an interview. hope it can help. if it is just press thank you )