I have bought boxes but never cases....do you end up paying additional Tax when it's over $1000 do you?
Richo - you pay customs/duties/taxes when the declared price of the import is over $1000AUD including the shipping cost. Even if you send in two different shipments within a couple of days of each other, they will just combine the packages and slug you the fees

There are ways to work around this. One of them being marking the parcel with a declared value lower than the $1000 limit. Finding a seller willing to do this isn't always easy.