I was in this position once with a UK buyer. It turned out that I had written his address wrong, so you should make sure there is no error on your side. As we all know, Australians are thoroughly honest, nice and incorruptible people who would never take advantage.
The buyer has been pretty understanding so far so you might be right about Australians. However, in this case, I printed the label directly from eBay so there was nothing I could mess up.