No offense, but this is really easy.
Dispute the charge with the credit card company, this takes about a month.
There's 2 things that can happen:
1. He doesn't fix it, you supply the tracking number of the return, and you get your money back.
2. He DOES fix it, supplies the credit card company the info, and you get a working watch.
/thread it's really that easy, the circumstances and events surrounding it don't matter in the slightest