It seems I have my answer, and it's at the bottom of Roxbury's page.
https://roxburysnumismatics.com.au/pcgs-grading/Quote:
There is an additional clearance fee for any Chinese items going over to PCGS for grading. This is due to Chinese coins and banknotes requiring additional clearance through customs.
The fee for Chinese items that require additional clearance is $350AUD per shipment.
Where possible, this fee will be shared evenly among all customers submitting Chinese items in that shipment. If only one customer submits Chinese items during that period, the fee will apply to that submission.
I had a 1902 Hong Kong coin and 1949 Chinese banknote in my submission, but the person I spoke to only mentioned the coin as being a problem. Perhaps they had not yet seen the other form, as both should be affected.
Looks like it's a broker fee for Customs clearance rather than a tariff. Still, it's very annoying that Chinese products are being singled out for some reason. Anyone else had this problem when sending Chinese products to the USA?
Things get complicated with where a product was actually made. My coin was made in England even though Hong Kong is stamped on it, but it seems that doesn't matter.
https://en.numista.com/15287Mint:
Royal Mint (Tower Hill), London, United Kingdom (1810-1975)