Hi,
One Customs officer needs to assess hunders of courier shipments in a day.
He will not have much time for every individual consignment. Normally he will assess his based on his prior knowledge of such products.
Usually it is on market price and not the price which the importer has bought it.
If the officer has some doubt about it, he googles for the price of the product and values accordingly.
But if it is just one peice, he will not waste so much time, maybe a few seconds or a couple of minutes max.
A courier company submits 10-15 parcels containted in one bag on the same sheet and if one is held for further evaluation, the whole bag will be held up. So no courier company is going to dispute the claim of the officer for one consignment and promptly pay the duty and recover the same from you.
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Devesh