Sometimes it is worth it to register for the GST even if you are under the $75,000 threshold.

If you sell to businesses it may increase your sales as they prefer to buy from sellers who can issue a Tax Invoice so that they can claim the GST back. And if you buy all your stock in Aus you can claim back the GST paid on it as well as any GST included in your packaging, postage, other expenses. You should speak to your accountant or tax advisor to work out whether you need to or choose to apply for GST.