Unless you have an inside source your best deals on pre-owned watches will be found here in the USA.

I have purchased several Rolex's and other high-end watches from a guy named Lawrence in Florida. He is well-known on Watchnet forum (feel free to check out the "good guys" section) I have been extremely pleased with his service and the watches. His prices are the best I have ever found for a pre-owned Rolex and he describes the watches very accurately. I have always been able to sell the watches for what I have paid for them.