I have to agree with this. I did a little digging on this seller. If you go to advanced search, check the box that says completed listings, then put in the seller's ID and search you can see everything they have sold. It blocks the buyer ID (the private part) but you can see the items as well as the winning bids etc. This person sells a lot of stuff other than Disney pins including Hard Rock and Olympics pins. I have a few Hard Rock pins myself, and the ones in their pics look pretty bad in comparison and so do a lot of the Disney pins they are selling. To check if I have the right person, the Alice keyhole listing I am looking at from a UK seller had 14 bids.
Besides thinking you have a fake, technically the seller violated eBay terms of use and should be reported. By offering you the supposed PP pin, the seller gave you an item that you did not buy. Legally it is called a Bait and Switch scheme and it is against the law. You thought you were buying a very specific pin, the LE 250 pin from the mainstream set of all 250 pins. You never bid on a PP pin. They never should have offered you that. And think of this; they could offer you a PP version, knowing you most likely never have seen a PP before to compare it with, let alone a PP of this pin. Therefore you have absolutely no source of comparison for authenticity and the seller knows this. In fact, they are banking on the idea that you think they are absolutely amazing for giving youthe PP of the pin, and that they are being so nice to you and helping you out just to throw you off. Go look at how much PP sets sell for on eBay and then think about how it would be financially responsible to hand over a true PP "just to be nice" for the same price as the mainstream pin.
On your end, you really have no way to compare it to anything. They very easily could have taken a gold backed fake and stained it black; it would explain the odd coloring on the pin back too. There is a chemical you can buy that is used to turn gun metal black and it is permanent. 30 seconds with a paintbrush and this dye and no one would ever know the difference. Please, do us all a favor and turn this person in for the bait and switch to ebay.