This scenario points out a downside for sellers on eBay. It is possible for someone to buy and item, purposely damage it or better yet, claim the got an "empty package", just to get a partial or full refund. This seem to happen more often with small electronics, like apple products. I guess you have to believe that people are basically good not to be overly paranoid about this practice. I would think with a hard to find item like a rare comic book, people want the item and purposely damaging does no good.

Anyway, if they are asking for a partial refund, I'd be inclined to think this is a legit problem. If even after a partial refund your still making a profit, I'd go ahead and do it. It's better just to get the problem resolved done and move on. If a partial refund now eats into the cost you originally paid, I would tend to stick to returning the item for a full refund. Now, assuming the later, you be getting back a damaged comic book. What is the new value? Will it take a long time to resell? Relisting may not be worth the time and effort rather than the quick partial refund.

Now, if your planing to regularly use USPS Priority or Express, ship comic books in a box. You can get them for free (order from the USPS web site). I'd still add some care and extra stiffness in the packing, but a box will go a long way for protecting it. It also look impressive to the buyer, which can help with feedback.

Always require buyer to initae returns through the Ebay web site. This give more protection for you. Even if you decide to just refund money without returning the item (I've done that with cheap items), this still makes it official and you'll at least get back any listing fees you paid.

Insisting on a return may require you to pay for that return shipping. Ask eBay customer service for help if you need help with the process.

I hope this helps. Good luck!