for what its worth
If you look at the pics of the silver arrow, and then look at the current stock of courtyard cars especially the jaguar currently advertised, the background is the same in that the wall and building behind are the same.
To me the wording of the advert is that of a trader, and the photo's similar to those of his stock. It looks with only a few cars for sale, he's a part time trader.
If he gave you a receipt with a company name on it instead of a standard home written receipt, then i would guess its a trade sale.
As already recommended i would contact trading standards in that area, who knows he may already be known to them. I would certainly also be opening a case with E Bay.
If he is a trader he should behave as one and provide the cover you are entitled to. If he proves its a private sale, then so be it.