Possibly i'm wrong about this, but according to one of the folks at our local Post office, the USPS will only insure up to the declared value. So if you declare it at a low number, you are taking a risk that should it get lost or stolen, you are out your 10k less the declared value.I don't know
I would have the seller declare it for it's full value, take photos of the watch, the watch iside the package, the watch packed in the box, the box closed, and the box with all the labels on it. That could help to substantiate your claim should a loss occur. Another thing that I have done in the past when shipping some precious stones,sent to me for approval, back to a jeweler was having the UPS manager personally inspect the package to actually see what was inside. in fact they required that since i was insuring the package for around 8k.The manager signed and affadavit to the effect that the package contained the stones.Of course, i could have replaced the real stuff with fake stones, but at least he was satisfied that there were stones n the package.