There is a lot of misinformation here. I wrote this a few years ago on Photo.net and I do not think the situation has changed.
I suspect that the real answer to the OP’s question is that it is a crapshoot. You do not know how you are going to get treated, and it should not be this way.
Like "Larkis", I am talking about importing into Canada but I suspect the same issues apply the other way round. A number of misleading comments have been made here which deserve clarification.
Firstly “camera gear should not be subject to duty”. Well maybe. Duty is based upon the “Country of Origin” and whatever trade agreement is in place between that country and the receiving country. For cameras, most have a Country of Origin of Japan or Malaysia etc, not the USA. When a US importer receives a camera from Japan, duty is paid at that time. If a Canadian then imports that same camera from the US, a second round of duty is payable!
The great NAFTA agreement, which decimated Canadian industry, states that there should be essentially zero duty between goods shipped among Canada, USA, and Mexico, so long as the Country of Origin was also one of those three. Also, and it is a big also, to qualify for the zero rate you must comply with NAFTA regulations including a long series of forms, among which you designate the Country of Origin, the Value, the Tariff Code, and the Tariff Treatment.
Professional importers know how to do this stuff, but private individuals usually do not. The bad part is that if you do not comply with the NAFTA regs then you default to non-NAFTA trade. This is where most of you are getting caught.
The default “miscellaneous” duty is 25%, so you are usually relying upon a wonderful public servant to look up the correct code in the huge code manual and apply the right factor, when he doesn’t have to! The application of the rules is entirely random with no apparent rationale or oversight.
UPS and Fedex often (but not always) handle this sort of stuff for you and charge a “Brokerage Fee” for doing so. I have just received two separate UPS shipments from the US – one was from New York and cleared customs at Fort Erie, the other was flown from Chicago to Toronto International Airport. The first one had a brokerage fee, the second did not, so go figure.
The UPS form shows a variety of potential charges – sales tax, duty, excise tax, brokerage fee, tax on the brokerage fee!, a freight collect charge, and a “permit” charge. A tad complicated.
Ironically, whenever I purchase from Hong Kong (shipped by UPS air) I am never charged duty or brokerage. However with UPS truck from the US, I am usually charged both.
Perhaps someone from the industry can comment better than I can.