Sold a dress on the 28th May on a buy it now. Sent it the same day by royal mail signed for. Contacted by seller a few days ago as she said she hasn't received it yet. So I traced it to her local sorting office and suggested that she contact them and collect it. Had an email from her last night saying that she has been to collect but they don't have it. I have just called Royal mail (don't get me started on how many buttons I had to press to get through to them!) and eventually discovered that the dress was signed for on the 30th May by the buyer, they sent me a copy of her signature and I have emailed it on to her.
So I suppose someone else could have signed for it but it seems unlikely, strikes me that she is just trying to pull a fast one. But what happens if she continues to deny it and makes a claim to eBay? I'm damned if I'm willingly going to give her the money back 
but in my experience so far eBay always find in favour of the buyer.