I had an issue, as a buyer, very recently. The item was not as described. I was frankly flabbergasted how quickly and decisively eBay worked in my direction. A little too quickly. (There were issues with my purchase that could have been fixed with a partial refund, but instead I got everything back, while I still have the item. I actually feel a little bad about it, like I don't want to use eBay again, even though they probably think they made me happy.)

Exactly. It doesn't make sense unless eBay just considers all sellers to be high volume resellers who write off small item losses as part of doing business.

If they actually had to devote much resources to investigate our claim, they would probably lose money on the transaction.

But, really, it's okay to lose money on some transactions, especially if you reduce buyer/seller stress on other transactions.

What I don't understand is why using this passphrase doesn't obligate the buyer to return the item.

THIS.

Except, I suppose, how do you validate THAT?

If I'm the seller, and you send me back an empty box or an old iPhone 3GS, what do I do then?

Just also tell them, "Item not as described".

Item not as not as described