I've been trying to ship a watch with insurance to Europe from the US, and it isn't as easy as one might imagine. If one chooses to ship with USPS, then it's not possible to add additional insurance to a registered airmail package, and watches are not allowed to be shipped with express mail, which leaves Priority Mail International, but insurance can only be added if one doesn't use the small flat rate box.
So, to ship a 9 oz box containing a $200 watch with insurance costs $40, compared to $10 by airmail without insurance, or $17 by priority mail small flat rate box.
It's not that I'm unwilling to ship internationally, it's just that most international buyers have no idea how much it costs to ship with insurance, and are likely to balk at the price of shipping, and otherwise try to negotiate more aggressively on the price. I also require payment by Paypal gift for international shipments, since the tracking by the postal service isn't enough to satisfy Paypal for the purpose of seller protection. And, when I let them know that I'm not responsible for customs fees or seizure, or loss (unless insured), they tend to disappear anyway, so it's really much more effort than it's worth.
Yes, I know all these conditions make me sound like a jerk, and honestly it's usually much easier to just restrict sales to within the CONUS. The lack of accountability and tracking in international post, the potential for customs issues, and the nature of Paypal rules is such that I much rather leave the watch unsold than risk having a Paypal dispute on my hands, and being out the watch as well.