It's really not that confusing. Here's how it works . . . when you buy the fish, you chose one of the US transhippers. You tell the seller who to send the fish through, and then you email the transhipper and make arrangements for the fish to get from them to you. The transshipper is licensed to import wildlife into the US and will clear the fish through Customs. Julie Tran here in CA charges $6 for this. Since she's only 40 minutes from me, I pick my fish up, but if I wanted her to ship them to me, it would be another $35 for express shipping.
There are multiple US based breeders and importers who also sell on Aquabid (my crowntail came from NY). When you look at the auctions, you will see an American flag next to the fish that are already here in the US. For those, you'd just pay the $35 and your fish would show up at your door.