^ that kind of thinking is bound to get you ripped off in the future.
it's 100% a rep.
I very much doubt it would get me ripped off with that particular seller.
Everything I see appears the be completely legitimate (excepting the tastefulness of the piece)
So you think an established watch and diamond shop in the jewellery district in Philadelphia, that has also been on ebay for more than 10 years, selling lots of watches up to and over $5000, with 100% feedback, and also listing a stack of obvious gen watches is going to sell a rep with 10 carats of diamonds all over it?
Why would he?
As psychologists say .. past behaviour is the best predictor of future behaviour.
He is offering a guarantee and everything I see about his ads suggests that the buyer won't need it.