If the parcel is caught on its journey, you will be billed for underpaid postage. If you do not have your 'sender' address on it, the buyer will be billed for the extra when they pick it up.
Aust post has installed some kind of funky machines that picks up parcels on their journey. It checks the bar code scan and parcel weight/size on its way through the machine.
The parcel you sent is not the correct size for the flat rate postage price offered.
Do this test:
With the parcel you have in your hand ready to send :
Go to Aust Post Calculate postage page.
Key in your postcode and the postcode you are sending to.
Put in the weight of the parcel, and the size (W,L, H). This is what is called cubing. Parcel dosen't go on weight but on cubic size.
Click on Regular and there you have the price that the parcel will cost to post.
It will be far different from the flat rate product box.
I speaketh from experience.
At Australia Post we are constantly striving to improve the efficiency of our operations and to make it as easy as possible for you to use our services. This is why we have partnered with eBay to provide you with the ability to purchase postage for your parcels online and at a lower cost than if your parcel was assessed and processed by our retail staff. We have also recently introduced Dimension Weigh Scan (DWS) equipment that measures and records your parcelโs length, width, height and weight during processing for comparison to what is expected for the label.
As you have paid postage online, this equipment also enables our retail staff to simply provide you with an acceptance scan when you lodge parcels. Not having to perform a full compliance check of postage paid articles is an initiative to provide you with speedier counter service and reduce the time you and our other customers spend queuing for service.
The DWS equipment we use is certified as Legal for Trade by the National Measurement Institute (NMI) of Australia. With this equipment, errors in application of paid labels, such as those you purchase on eBay, will now be routinely detected during processing and underpaid mail invoices issued. We will be assessing articles processed in a calendar month and invoicing for underpaid postage, plus an administration fee of $1.50 for each underpaid article, in the following month.
In relation to your parcel, our assessment is that you are selecting Parcel Post flat rate (standard packaging) label when you should be selecting Parcel Post Parcel (own packaging) label and declaring the dimensions and weight of your package.
With your parcel, reassessed charges are based on the dimensions rather than the physical weight. Please refer to our size and weight guidelines at http://auspost.com.au/parcels-mail/size-and-weight-guidelines.html for details of how cubic weight for domestic parcels is calculated.
In regard to using Australia Post flat rate postage labels with standard packaging available from the Australia Post eBay store please check the following link http://stores.ebay.com.au/australiapoststore.
Had one parcel get caught out. It was in the correct sized box but was not a Aust Post printed box. (was a cleanskin B2 box ).
In my case, they sent the parcel on but billed me for the cubic weight plus the admin fee.
