Hermann,My Omega Seamaster from a Ebay seller in Japan was a good deal. Certified genuine and by what I can see the watch had rarely been worn. I know it was real because it has patina on the hour hand, no fake seller would patina a fake. the casual underinformed buyer, who is looking for perfect, would never buy patina on a $2000 watch.
Please post a picture of the watch you purchased! I am clueless on high end/ collector watches.