You can't trust Trademe and their book courier fee option. It appears they update those fees once in a while, rather than realtime. It happened to me numerous times, so now if I am prepared to courier something, I choose "I don't know the costs yet", and if person insists to know beforehand, I tell them that this is current fee showing by Trademe, but it cannot be trusted so it may be few dollars more, and if they want to proceed on this basis all good, otherwise no trade.