Why is it important for marketers to understand post-purchase evaluation as the product or service has already been purchased? Feedback after purchase is the most reliable way to collect information for new product development. The marketer needs to understand behavior before, during, and after purchase to build relationships for future business. With careful consideration of the post-purchase behavior, the marketer can help avoid lawsuits from dissatisfied customers or warranty returns. Collecting information from the purchases and post-purchase behaviors is the most reliable way to gather data about using the General Model of Customer Behavior.