There are basically two approaches you can take: Ask them (“Stated Importance”) or Derive it (“Derived Importance”). dive into the article for details...
https://www.genroe.com/blog/how-do-you-determine-what-is-important-to-a-customer/440/
In order to design a series of questions that will specifically address the purpose of conducting the survey can turn into a messy business. Companies are unable to obtain accurate and quality responses from customers because many customers tend to lie or exaggerate during a survey. This causes inconsistent results and companies are unable to benefit from the research. However, research remains to provide solutions to these survey problems. Here are 10 tips to consider when you design customer feedback surveys
https://tech.co/10-important-tips-consider-designing-customer-feedback-survey-2015-07/
We’ve all experienced that person who’s talking on his cell phone in public, in a voice that’s way too loud — on the train, in a restaurant, or walking down the street, screaming into the mobile, oblivious to the effect he's having on the crowd nearby.
We rarely experience this with a land line phone. That’s because when we talk on a land line phone, “There’s a small percentage of our voice that’s fed back to us. It’s called "sidetone,” according to former Bell Labs scientist Dr. Steve Crandall. About 18 decibels of sound (the loudness of a whisper) comes back to us to give us an indication that our voice is being heard on the other side of the connection. When we have that feedback, we are less apt to make a spectacle of ourselves.
http://mashable.com/2010/06/20/feedback-filters-social-media/#siIC_vhwS8qi/