sbiddle: I've probably purchased ~30 items from China in the past year. Everything has been marked as a gift and the value under declared. None where over the threshold anyway so wouldn't have incurred GST or duty, but it's clearly the norm for many shippers.

So, would you be honest enough to go back to customs and inform them if any under declared goods were over the threshold? 

It is theft not to do so right?

[edit] I expect people do not correct customs when under valued goods are received, and customs may not even have procedures to correct these anyway.