Here is a post at another site:
Recent posts about import duties prompted me to do some research on this issue. Here is what I found:
All watches imported to the US are levied 5.1 cents per dollar specific tariff. So, if a watch costs $100, the specific tariff is $5.1. But wait, that is not the end of the story. There is also an "Ad Valorem" tariff, 6.25% on the case and strap (or bracelet) and 5.3% for the movement. How the custom agent determines what percentage of the declared price is the case and strap; and how much the movement worth? God knows.
But then, if the item is shipped through the post office (registered mail, post office express mail - EMS, plain surface mail or air mail), the package is eligible for a duty wavier if the declared value is less than $200 for goods that you mail back to yourself while travelling abroad, or less than $100 for gifts that are sent to you by someone else.
To make things more complicated, if the item is determined to be something that the recipient can resell, there is no duty waiver. Oh, also if the recipient receive multiple items on the same day and the culmulative value of the items exceed the waiver limit, all the items will be taxed. (Time the shipments accordingly?)
The duty waiver is not applicable when the item is shipped by courier services, such as FedEx, UPS, DHL.
Ok, so here are the different case studies:
Case 1:
You are travelling in Japan, came across that nice Seiko, bought it at the store and mail back to yourself through the Japan Postal Service. On the custom form you wrote down the declared value of $200 which is the price you paid for it at the store. You are eligible for duty waiver if the watch actually worth only $200, and there will be no import duty on the watch. If through inspection at the US custom, they open the box and found out it is a $3000 Grand Seiko instead of the price of a Seiko 5 declared on the form... Then you are in serious trouble.
Case 2:
Same as case 1, but shipped through FedEx. Since items shipped through courier services are not eligible for duty waiver, the $200 watch will be assessed the $10.2 specific tariff and depending on the custom agent's assessment, the Ad Valorem tariff will be tagged on, let's just say all $200 of the cost of the watch goes to the case and strap and the movement costs nothing, then an additional $12.5, that is a total of $22.7 on the $200 watch.
Case 3:
Bought the same watch through internet for $100. The seller put down $100 as its declared value and shipped to you through the post office. Since it is eligible for the duty waiver, no tax is due.
Case 4:
Bought the same watch through the same internet seller, paid extra to ship it FedEx. Un-oh, not eligible for duty waiver, so you will get billed by FedEx for the import tax of $11.35.
I am not suggesting you to ask the seller to change the declared value when shipping the watch you purchase so that it is lower than the waiver limit. For that is called fraud, if you get caught, you will be heavily fined and could do some jail time. Custom agents can open any package that enter the country and will check if the item matches its declared value. Obey the law and declare what the watch is worth.
The tax rates that I quoted could be outdated, I was not able to look up the latest Harmonized Tariff Schedule, if you are interested go google HTS 2005.
Hope this will help clarify some confusions. But before the end, some disclaimers...
Disclaimers:
(1) I am not an expert in import tariff, the above are just information I gathered through my research. The accuracy of the information has not been verified. Use them at your own risk. Consult US Custom for the official explanation of this issue.
(2) I in no part advice any person to intentionally declare the item shipped at a lower value than its actual value or fair market value so that it is eligible for the duty waiver. Doing so constitutes a criminal act and is punishable by law. I am not responsible for such an action taken by any reader of this post. I strongly encourage people to abide by the law.
I can even remember trying to look this up on USPS website and couldn't find anything. 
