Amazon Accepting Incomplete Returns - FBA

We are a brand that sells socks, and we have noticed a significant percentage of the returns we get back from Amazon are missing pairs. For example, only 2 pairs inside the packaging when it should be 3. It seems customers are buying the socks, keeping 1 pair, and returning the rest for a full refund, and Amazon are not checking at their end.

Does anyone have experience with similar issues and is there anything we can do?