Sorry for the late response, I first make sure that I put the opposite person in a position where he feels like he has more knowledge than me in the topic I'm about to ask, this shuts down their defense and opens them up, "Hey, a friend asked me the other day, but I couldn't give him an answer I'm sure you have the answer do you have an explanation why the prices in the offer sheets are much higher compared to four years ago...." Once he tries to explain, you can direct the flow of the conversation by follow-up questions if you give him hints, they should always come from a fictitious third person this way he never feels threatened by your knowledge and still thinks he has greater knowledge than you.