I have seen a few watches on watch rapport that I've been drooling over but those nightmare-from-hell reviews have kept me from going forward. Watch Rapport seems to be an eBay-style site in that they are a middle-man between buyer and seller but they seem to have no accountability when things go south.
I have bought a couple of watches through Chrono24 and both were a good experience. If you buy from one of their registered dealers, Chrono24 holds the funds in trust for a few days so in case you have any issues, they return your money directly before the seller can run off with it.