if the value is more than AUD800, you will have to pay GST & custom/duty tax
they calculate the custom tax on the item value plus shipping cost, then they add GST on top
so if your item is $1100 in total, custom tax will be about 5% (it varies, pls double check) comes to $1155
then they will add 10% GST comes to a total of $1270.50
thats how i calculate the tax when i sent a container from overseas to here
best to ask the seller to declare the item value to less than $800
hope it helps