I just sold a few items on Ebay, all nice dresses that I have decided are a bit young (i.e. short!) for me now. Everyone paid (eventually) and I posted using Royal Mail first class as indicated on the listing.
Out of 5 items, two people have come back to me. One asked for the 'tracking number' so she could track delivery. She hasn't actually said it hasn't been delivered, and all the other items posted at the same time have arrived safely. She knows there isn't a 'tracking number' bc its first class mail, untracked. She likely also knows that if she complains to Ebay they will 100% side with her even if I show the postage receipt and she will get a full refund. I know this because it happened last time I sold things on Ebay. Do this many things really get lost in the mail?!
Another girl sent me a very short message alleging that the item wasn't as described because it didn't fit her and therefore I must have shrunk it so she demanded to return it. I replied to say that I hadn't shrunk it as I hadn't washed it (it was silk) or even dry cleaned it as had only worn it once or so (this is all true, it was in as new condition). I said usual Ebay etiquette would be to accept things don't always work out when you don't try them on in a shop, and simply sell on. She said it wasn't the same as her other items from the same brand, therefore wasn't as described and she wanted to return.
I was pretty pissed off by the pair of them, and decided enough was enough. By chance buyer 2 works in my industry but is more junior than me, and I am now client side and head of the function. I therefore wrote back very sweetly and said that I was 100% sure that the item was as described, the listing had stated no returns, and I didn't really want to refund her. However, I said, "as it happens I am due to meet one of your senior colleagues next week at your offices so I would be happy to meet up with you beforehand so you can show me your existing item and how the sizing differs and then of course you can have a refund." As I happen to be looking for some professional advice in relation to a big project, I also emailed one of her senior colleagues to set up a meeting just in case!! Funnily enough she replied to say not to worry about it and she hadn't realised it was no refunds and she would try to sell or give it to a skinnier friend! 
AIBU to think that people are really naughty and completely trying it on?!