You could try calling ebay Customer Service to ask for Feedback Removal if it looks like there was grounds for Extortion in your ebay Messages.
Does his Feedback for Others indicate he's impossible to please?
By making reference to something in the ad that wasn't actually there, your buyer might have fallen victim to the email that ebay sends sometimes to people telling them a similar item is on sale at a better price. If that buyer doesn't actually LOOK a the link sent to them by ebay, he or she may well end up buying an item that's not what they intended. There is a thread here http://community.ebay.ca/t5/Seller-Central/Ebay-emailing-buyers-with-better-deals/m-p/318843#M51602. You'll have to review your messages from the buyer to see what he or she says and whether it fits.
Or you could leave a Follow-up to Feedback indicating the buyer was mistaken. Don't fly off the handle with that. It would only make you look bad.
Or you could add this buyer to your Blocked Bidders list, and spit twice in his general direction and simply move on like pierrelebel says.
I'm more of a fight-till-I've-dropped person much to my general demerit. Pierre is wiser than I in most ways.
In the end, it happens here and it's not fair. It won't matter much after the Spring when new seller evaluations come into play.
You can't please everyone. Some people can never be made happy.
But I'd question him about the reason he thought this train was something else first.
