Oh, another great story. So my supplier was doing something called double invoicing (or something like that). He would charge me $xx per unit, but then supply a lower cost to CBP so that I could save money on import duties. They never told me this. And I don't know what the fuck I'm doing, so really never looked. Once I figured it out, I freaked out. If CBP figures this out on their own, the fine is something like 300% of total retail cost of the goods.
So I ended up paying like $5k in make-up duties and penalties. And another $5k for a lawyer to handle it. I'm such a small importer, I probably could have just gotten away with it and moved on, but I'm pretty risk averse.