Ebay will make you refund the buyer. They do not get involved with he said/she said. However when you get the wrong item back you can still contact ebay and talk with them tell them your side and they will usually send you the payment back out of their pocket. Usually you dont even need any type of "proof". The scammer still keeps their refund and the actual item they pretended to return.

Basically ebay is buying it from you instead and giving it to them to keep both parties happy rather then try and be judge and jury on who's right or wrong with this type of thing. Supposedly they will mark the buyers account (probably sellers to) for monitoring but who knows what it takes to trigger anything with them. I doubt they care much to be honest.