1. If the price appears too good to be true, then it likely is.
2. Be very careful on sites like ebay. Some sighs to be wary of are the use of blurry low resolution images in listings, lack of details in descriptions and sellers with little or no feedback.
3. Just because the watch comes with an authentic looking box manual and certification it doesn't mean that it is genuine.
4. Buy in store follow your instincts. If the decor and location do not fit with what you would expect for a luxury high value item then don't take the risk.
5. Have the watch inspected by an expert, often better fakes require inspection of the mechanism to tell them from the real product.