I remember as a seller once I accidentally sent the wrong item. It was an item I wasn't meaning to sell, they just got confused. The buyer refused to return the item and caused me a lot of hassle over it. I never did get it back, and later had to replace it. While it was my fault that that occurred, I would have been quite happy to send the right item at my expense if the other was returned, and reimburse the shipping. It's the only time I acciidentally sent a collection item by mistake and I've been doubly careful since, because there's no guarantee that the other person in the transaction will want to straighten things out.
I guess for a cheap pony, maybe the seller figured cutting his losses was better.