When does a credit card get verified if a product has a free trial period?

Credit cards are verified at the time of signing up for the trial even though the card isn't billed. This can be demonstrated by attempting to purchase the trial using fake or invalid credit card information. Even though the card is verified it's still possible that when the card is billed there are insufficient funds. High failed payment rates are a standard component of running a subscription business. That's why MemberMouse has automated overdue payment handling built in: Automated Overdue Payment Handling