It seems a bit.... out there.

What kind of ads were they replying to? High value ($10K+) pieces?

Is it just they'd pay for your flight to Rotterdam, meet you outside this unassuming jewellers, and then - well - bluntly - have you set upon by accomplices who rob you of the watch? You'd have to be pretty daft to fall for this though, no?

Doesn't really make any sense for lower-value watches, mind. Perhaps I'm missing something really obvious.