Reach out to both "good" and "bad" customers. You don't just want to talk topeople who love your product and want to spend an hour gushing about you (asgood as that feels). Customers who are unhappy with your product will show otherpatterns that will help you form a solid understanding of your personas.
This is our number one thing we look into since for where I work at we primarily offer a service. We constantly review our reviews on google, surveys and our message bored. More importantly we look our members that aren't satisfied and see it as an opportunity to grow and improve. However, we also do understand that our facility not be for everyone.