I have had a similar experience *non comic related*. Unfortunately eBay will never side with the seller as long as the buyer maintains innocence. That's all the scammer has to do to game the system. If they don't admit to any faults, the seller will 100% lose the case and they will force the seller to refund the buyer including the return shipping cost. eBay states that they are only a 3rd party and can only go by the evidence presented within the messages within their system. They cannot verify what the seller sends to the buyer and will not look at anything else or consider any evidences outside of that scope. Judging from the responses I am reading, it seems most people don't realize that seller protection on eBay is barely existent. Again, if the buyer does not admit fault, the seller will lose the case flat out. Bottom line, DO NOT sell anything you can't afford to lose on eBay. As screwed up as this sounds, cases like these don't happen that often, but you will eventually run into this if you're a power seller.
As for the OP, your only option now is to gather as much evidence you have and determine if you have a case to take it up a notch to authorities or bring the culprit to court for dispute if you think it's worth the time and effort.