As mentioned above, if the item would incur more than $50 gst (12.5% of $400 is $50) and it gets picked up, you will get sent a letter requesting the payment of gst plus any other levvies.They wont release the item until this is paid.
It you use a business address it is very likely to get picked up, but if you don't, most of the time they seem to slip through.
I have heard if the sender ticks the box saying its a gift then you wont get charged gst.
At the end of the day, bank on having to pay gst. If it slips thought, consider it a bonus.