I am glad customs did not look at this. USD 9.20 is way too low ... in Germany you have to pay about 100-150 eur if you cheat at customs and get caught.
Just for your information, when technobit send their first batch of HEX16A, my board stuck on speedy office for more than 3 week because marto issue full prices invoice. Speedy demand marto to issue low prices invoices(Proforma Invoices).
The 10 USD per board is my suggestion
My second order HEX16C use UPS as carrier & i didn't find any invoices but marto declares the miner as SAMPLES
And again no import tax Since the miner come with no case, then there is no problem declaring it as SAMPLES(which should be free)
Low prices = No import TAX = Quick custom clear