You said that the person who bought the item off of you is now listing it for sale on his own eBay account. When he listed it for sale did he list the item as being in perfect working condition, or did he list it as not working? If he's listed it as being in perfect working condition make a note of the item listing number and contact eBay Customer Services by clicking on this link https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid and click on the blue button that says "Have Us Call You", located at the bottom of the screen. The best option would be to contact eBay first thing in the morning when the lines open, as that way you've got a better chance of getting a phone call from an eBay representative in Ireland, rather than receiving a phone call from a Philippines-based eBay representative, which you may well do if you leave it until the afternoon or evening. Give the item listing number to the eBay representative and explain what has gone wrong. If the seller has claimed that the item was not as described, claiming that it was not working and subsequently gave you negative feedback to that effect but is now selling it as being in perfect working condition, then you may be able to get the original decision overturned and the buyer's bad feedback removed from your account.
In the event that the buyer is listing the item as only being suitable for parts then you may have a harder time getting the buyer's feedback removed. However, it may still be worth a shot - just because you were unlucky the first time doesn't necessarily mean that you will get unlucky twice. The person you speak to the second time may well see things differently from the first person you spoke to and feel that you have a justifiable reason to ask for the negative feedback to be removed. However, if you don't try you won't know whether you could have got the feedback removed by being persistent and refusing to let the matter drop.
If you have not already done so by the time you read this reply add the buyer's User ID to your Blocked Bidders List so as to prevent him from purchasing anything else from you in the future and causing you any further aggravation.
