Where is my parcel?
As a long term eBay seller I have had that question sent to me many times and as an equally long term buyer, I have had course to ask it too.
Please remember that late parcels are not always the seller's fault. If you need to ask about a parcel, first ascertain that the seller has posted it and when. Once a parcel is in the postal system the seller has absolutely no control over it.
The post office or post offices are your next step, start with your local post office, your parcel may have been 'carded' and waiting for you. If it is not at the post office, you or your seller can initiate an enquiry from either end, you will need a 'Customer Service Complaint' form. Fill this in and lodge it at the post office, you will be given a slip with your reference number on it, don't loose this.
In Australia you can register a parcel which carries $100 or more worth of insurance and/or you can ask for recorded delivery which will require a signature but also has a traceable number.
If you don't have registered or recorded delivery all is not lost, you can still claim up to $50 from Australia Post if you have the right proof, this is usually details of the value plus proof of payment and postage. You will need these from your seller so remember always try to be polite and pleasant.
No good ebay seller (check feedback) is going to deliberately cheat you, risk negative feedback or a strike, most will bend over backwards to help you so please remember, it costs nothing to be nice and will get you far more help than an angry aggressive email will.