Unfortunately eBay is very one-sided when it comes to selling, as they tend to lean very heavily towards the side of the buyer. There are some steps you can take, though, which ought to help reduce the chance of this happening again:
First of all, if the item has been returned to you then refund the buyer's money in full (including the extra that he/she asked you to pay for Special Delivery). However, if the buyer has opened an Item Not Received case then eBay would close the case in your favour as you could prove attempted delivery of the item - you cannot be held responsible for the buyer's failure/refusal to collect the item. As a result you would not end up with a defect on your selling account in relation to the transaction.
In the event that the buyer leaves you negative feedback in relation to the sale then get onto eBay Customer Services and ask for it to be removed, pointing out that the buyer failed to collect the item. You can use the tracking to back this up and prove this to eBay. That way you ought to stand a better chance of any negative feedback left in relation to the transaction being removed by eBay. If this were to happen the buyer's feedback would do no lasting damage to your account once removed from your feedback history, and the associated defect will also be removed from your account.
If you have not already done so, I would advise you to add the buyer's User ID to your Blocked Bidders List before you relist the item for sale again. If the buyer has messed you about once then what's to say that he/she would not do so again? Do you really want to take the risk of the same thing happening all over again with the same buyer?
Should you decide to relist the item for sale it may be worth readvertising the item at a slightly higher price than you advertised it for the first time so as to claw back the amount that you lost the first time. If you set the listing up with free postage then whoever buys the item next cannot mark you down on the postage costs being overly high, as eBay will automatically give you a five star rating for the postage and the question "How reasonable were the postage costs?" will not be available for the buyer to mark you on when he/she comes to leave feedback for the item.
