Customs may be an issue with regards to fees; if you're selling gens, you'll want to insure for the value of the watch. This means that you'll have to declare that value, and customs will leverage fees based on that figure.
In addition, declaring the value and/or content of the parcel may open up additional risk/liability; all it takes is for one unscroupulous individual in the chain of transit that decides taking the contents is worth the risk. So, be cognizant on how you fill out the customs form. Granted, insurance will cover the loss, but filling out forms, making claims etc. is a hassle.