It depends how you get it sent.
Generally, by using freight forwarders like UPS, DHL, TNT, Fedex, they will pay the GST/Import Processing Fees (if applicable) to Customs for you and you pay them. When you ship using this method, you are generally allowed up to and including AUD$250 before they start worrying about it. Anything over this, and they work out the difference.
If you use a common carrier such as Australia Posts' EMS, or the United States Postal Service (USPS), you have a AUD$1000 limit.
You pay duty on the dutiable goods, and GST on shipping, the goods' cost and insurance. Some stuff is dutiable, some not. Depends on if it's new, has been assembled, if there's competition in Australia for that item. For example, I own a snowboard company, and I do not pay duty on the snowboards anymore since Force started making boards in China and Austria i.e. there is no local industry to protect. Also when I brought some boards in with me back from Canada/LA, I got asked by the floor manager all sorts of questions that reduced my duty by half. I was totally honest and by asking me the right questions and getting the right answers, he reduced the duty. Things to consider for bringing MTB stuff in.
If it's been attached to a bike, duty is reduced.
If it's not for commercial sale (as my snowboards are), duty is reduced
All sorts of caveats like these exist.
As has been mentioned you can get the invoice emailed or fax'd to you, thus customs can't ascertain it's value...
Will they worry about something like this? Chances are no. I always get nervous and be honest though, mainly because I pass the costs on to customers, but since you're operating in a non-commercial sense, I'd go with the no-invoice option. If you're using Fedex I doubt they'll do it, as they are totally above board, so the supplier can jimmy up a false invoice. This is illegal and substantial penalties apply. You have to weigh up the risk/return factors.
Also though, USPS will be easier than dealing with a freight forwarder.
They will take the item and deliver. Getting a supplier to ship with USPS could be a problem, mostly they like to use Fedex and/or UPS.
Any other questions, email me at
contact@dirtsystems.com, got a bit of experience dealing with customs and also have contacts if you need, such as customs brokers etc
And, a shameless plug. Dirtsystems is a new MTBers apparel company I have started with a mate.
dirtsystems.com (sorry Admin, it had to be done)
-Cheers
//Edit: My mate just got stuff from Jensons and I don't think he got a call from Fedex. He paid Jenson, they paid Fedex, and Fedex delivered. Maybe if the shop puts "third party to pay" when I use Tolls I have that option.
Also if your total GST/Duty is under $50, customs will NOT GET INVOLVED.