Unfortunately, eBay does not do anything to unfair feedback. Such feedbacks does not fall under their removal policy which is outlined
Here.
So pretty much if you give a negative to a scam seller, you'll most probably receive a negative too. And you can't do anything about it.
However, there is
SquareTrade which is an online mediator. You can file your unfair feedback case there and they will try to resolve it. If it rules out in your favour, SquareTrade has the authority to request eBay to remove the negative feedback on you.
But everything comes with a price, it costs about $20 to be a member before they will take on your case.