I think it also has a good bit to do about how the seller fills out that watch worksheet. The movement is where most of the value of the watch is, however it's taxed the least. The case is taxed at one rate and the bracelet/strap another. So if the seller fills out the form with the vast majority of the sale price noted in the movement section, and say $200 for the case, $100 for the bracelet/strap, your duty owed will be greatly impacted. If they just split it in thirds, you'll pay more.
Here's another good read for you, they seem to lay it out fairly well.
https://theluxurywell.com/blogs/news/customsduties
And pardon, the link I sent before is a beast, over 4000 pages to sift through of the US Harmonized Tariff Schedule. Chapter 91 deals with watches and clocks specifically.
Click to expand...