How to enforce Amazon Return Policy - Video Games

Amazon Return Policy: Software and video games can be returned for a full refund within 30 days of purchase. Returned software or video games that are activated, used, or missing parts will incur up to a 100% restocking fee.

When I receive a video game back that is opened I submit a FBA Reimbursement request and it is denied due to the product being marked as "customer damaged." There is no damage. How can I enforce the Amazon return policy stated above?

I've even received back games that only have a digital download code in the box that has been used by the customer and it is denied as it was marked as "customer damaged."