In order to get someone to respond to an open-ended question with  more than "I don't know", we first have to establish credibility and rapport during the conversation. This takes good interviewing and listening skills, and practice. Some people might not really be engaged in the interview in the first place, but if you help them understand that you sincerely want their feedback, and allow them to really talk, you will get better responses. It may take a few questions to warm them up: "What were the key problems you were trying to address " is a good question. If you get an "I don't know" answer to that, you are either talking to a hostile person or the wrong buyer. We need to be empathetic to their situation and never try to "sell" them on us during this process. Even if they were misinformed during the sale. Now is not the time to try to convince them that we have the right product.

It is not dissimilar to conversing with a teenager. When I learned to empathize with my daughter and really listened to her without always trying to jump in with my advice, I got way more information than I really wanted!

Don't give up or get discouraged. Some people just want to get off the phone. But that's OK. For the ones you are able to engage in a conversation, let them talk. You may even have trouble getting them to stop!

Answer by Barbara Nelson