The buyer must first open up a return request through eBay ... any sort of claims or requests through eBay messages is outside of the return process.
Depending on your return policy, eBay may automatically approve the return ... or you may be asked to approve the return.
Once approved, the buyer has 5 business days to ship back the product. If it isn't shipped back, you can call customer service and ask them to close it, or it should automatically close anywhere between 15 and 35 days.
If the product is returned back to you ruined (or in a condition that is not what you sent), then two things can happen if you call eBay to tell your side of the story.
Thing 1 - Most of the time, the Customer Service Representative will simply tell you that they have no way of knowing if you or the buyer is telling the truth, and that you just need to refund the buyer. You can escalate the problem to a "case", and this will likely be decided in the buyer's favor and you will refund the buyer.
Thing 2 - There are times when Customer Service will side with you, perhaps because other sellers have reported the buyer in the past for abusing the Money Back Guarantee or returning damaged merchandise. In this case, eBay will cover the cost of the return. This latter thing happens very rarely, but it does sometimes happen.
Finally, if the buyer abused the Money Back Guarantee (lied about the return reason), or did anything that was inappropriate, then please report the buyer using the "report buyer" link next to the item on your Orders page.
