A sketchy cat is selling an El primero. Loacaly. And there is no way this was his. Figured I'd sleep better if I posted this.
On the off chance that it has been stolen,and the owner had retained the serial number and reported it to the police in his area, your sensible approach would be to contact the police in your area. That is, IF you have the watch, and you have the information from the guy who is trying to sell it! I don't know if there is a national data base accessible to police wherein serial numbers of stolen items are maintained.