I won a case on eBay where a seller never shipped an item to me the way described, in the time they said they would.
A few minutes ago, I got the package in the mail-AFTER I received a full refund and spent it.
You already have one so you obviously don't need it. The people who sold it to you might need the money they get from selling it, so send it back. I'm sure they'll be happy to have it found and be able to sell it again. They might need that money. But, even if they don't, it's a dick move to keep it.
You could get away with keeping the money, but would you be morally ok with that? If so keep it.
I'm pretty sure this doesn't matter anymore. This was three months ago.
Don't you love the way fucking eBay is loaded down with CPU wasting, bloated, ads? They are already making out on auctions, and are alienating customers who are there (surprise!) to buy shit, not look at fucking ads. I have an older desktop, and I can hear the damn CPU fan revving up everything I go to that shithole.