EBay has a Money Back Guarantee.
Not a reduced price for damaged goods guarantee.
Most sellers are willing to work things out, but some are not.
The MBG claim will get you a return shipping label.
Once the seller has the disputed item back in their hands, they are required to refund you for the whole purchase.
If they do not eBay will refund you and go after the seller for their money.
If you went to WalMart because the package of tube socks you bought had three good pairs and one pair that was missing the foot, you might get a replacement package or more likely your money back. What you wouldn't get is a reduced price on the packet you bought.
Same difference.