Faced a similar situation, not on selling any watches, but luxury goods. The modus operandi is the buyer will insist on their own pick-up delivery service (through DHL/FEDex). Then, they will e-mail us a transcript of a bank (FAKE/Photoshopped) from Western Union/Bank of Scotland with our details on them, insisting they will only release the payment once we wire customs fee(worth maybe 30% of the value of the item).
Please be cautious, friends, and block the buyer immediately.