I just sent him another PM and will give him a chance to answer. If he doesn't, I'll get in touch with the staff and even Paypal.
I still hope this turns out good...
Edit: He just replied... said he shipped last Monday and seemed a little [censored] off that I threatened to inform the admin staff. Well, I can understand that - but on the other hand, had he just replied to one of my previous two PM, I wouldn't have got suspicious. Especially because he was online every day.
Anyway, maybe I just expect too much... let's wait and see if the watch arrives.