They're fined because they lied on their declaration forms. Our customs agents are generally pretty fair and reasonable, but they do take their jobs very seriously.

Tip for travelers to Australia/New Zealand: If you have something that is stated on the declaration form, just answer yes. Provided it's not some totally illegal substance, they'll inspect the items and if it's not allowed past the border it'll be seized without penalty. Someone will correct me if I'm wrong, but I believe in some few cases, you can even pick it up on your return.

If it's something like large amounts of cash, goods, alcohol or cigarettes, you may have to pay a tax or import fee and answer a few questions. Just don't be a dimwit.