you greedy so and so - you never even paid for it, it was a gift.
Like I said, an item like this without warranty is worth significantly less than if it had a receipt/warranty. Given I have seen them go on Ebay for under $750 with GST, tax invoice and full Australian warranty, I think $400 is generous.
But hey, if a potential purchaser wants to buy an item that will almost certainly have to be repaired at some stage (like I mentioned - every O2 phone I have had - and that is 3 - have had to be repaired at some stage), for almost retail price but with no warranty, then you have done well. Gl with the sale