Why? A material change was made to the item after the point of import. This would be like taxing a timber importer as though they were importing furniture.

I use FedEx for work, and our account has heavily discounted rates for Priority services - not for Economy. That’s what I assumed was happening here, until I saw that you were dealing with them as John Q Public.

I doubt that the incinerator was big enough, and that’s what the “icky specifics” covers…