The watch has an ID/serial number. The record on the ledger is transferred to the new owner. If both new owners check the ledger, only one of them will have been assigned the watch with the corresponding SN.
the payment could even be done atomically with the assignment of the (authentic) watch. As long as the buyer validates it, the only one who could forge watches would be Rolex.
This. How does this magical transfer happen? The moment you say "authorised resellers", please read comments to this: https://news.ycombinator.com/item?id=27435785
> the payment could even be done atomically with the assignment
What's to stop an automatic payment with the assignment of the counterfeit watch?
> As long as the buyer validates it, the only one who could forge watches would be Rolex.
Why?
How do you sign a physical watch with keys?
> Let me ask you this; if you buy a Rolex watch on eBay that includes a QR code as proof of authenticity, how can you be confident that the same QR code has not been included with 100 other duplicate watches otherwise?
I can't be confident. So, once again, how does blockchain help?
> A correct blockchain implementation would have allowed me to spot that within minutes of receiving the package as well as irrefutable proof to present to eBay/law enforcement
- What's a "correct blockchain" and who implements it?
- How would it help if both watches/headphones/whatnot point to the same record in the ledger?
- more in two comments to this: https://news.ycombinator.com/item?id=27435785