That is reasonable, but that isn't how tax treaties are worded - they use fair market value. If you send an item with a price tag (or I send such an item to the USA with a price tag), and the item is opened for inspection, then excise, duty, and taxes are based on the price tag, not your (or my) valuation.

In reality, the importance of such consumer or hobbyist transactions is very, very low relative to more pressing border-related matters or business transactions (which is why shipping from a commercial address is more likely to lead to inspection). However, the flag must still be flown every once in a while, and people made an example of.