Customer feedback is used in a number of businesses to improve the products or services, to test new products or services, and to figure out what customers prefer or want. Simply speaking customer feedback helps a company in conceiving, designing and selling a product. There are a number if ways in which customer feedback can be obtained, including surveys, interviews, user activity and usability testing. Surveys are easy to design and spread around. Nowadays they can be designed online and customers can fill them at their convenience. One can also get feedback from customers, either through feedback books or boxes in offices or feedback sections online. The tried and tested method of door to door interviews can also be effective. For online services, one can also track user activity and figure out how to enrich their experience. Many times, businesses will actually give you gift certificates or something to incentivize the feedback process.
Hope this helps.