Of course goods that were intended to go from Europe to the Southern ports might not have been unloaded at all. I would suppose the Federal agents in charge of Tariff collection would simply inspect the cargo and manifest and then assign the appropriate charges based on applying whatever tariff under which the goods happened to fall.
They could probably find out if any ships were cheating on their declarations by the records kept by other Federal personnel at the eventual port where the cargo was unloaded.
Why don't you research this point further yourself and get back to us?
Of course, since this line of questioning will lead away from your preferred narrative, I will be surprised if you bother to learn anything. It's far simpler to sit there and carp about information other people (in this case, BroJoeK) found.
You don't know, do you?