Other duty info travelers may not know. It's $800 per person, no matter the age and if it's a family unit in the same household you can combine the exemptions. Above the $800 per person is a 3% flat rate for the first $1000. So a single person spent $1800, the most duty they'd owe is $30. Once you've gone over the $800 exemption and the $1000 flat rate, you have to use the harmonized tariff (HTUSA available online for all) to figure of the remainder of the percentages; which can have various rates for the different pieces i.e. the watch band is one rate, the batteries are a different rate and, there screen is yet another rate. Most Officers don't want to waste time with this and unless it's a substantial amount are going to give you a break at the 3% rate. These exemptions are for personal use, not commercial use.
Failure to declare any goods no matter the reason/cost, it's subject to seizure and penalty (10x the loss of revenue).
Harmonized Tariff. Harmonized Tariff Schedule PDFs
CBP Duty info Duty-free exemption, Gifts
