When someone comes to your product and asks questions about how it works, why it doesn't work, or simply complains about its problems: don't help them right away. Instead, fix the product while they are waiting "on the line," show them a new version of it, and ask to provide feedback again. This is how you use them as free testers and make your product become better.

The video is here: https://youtu.be/tI6rGQIevxU