I don't know Australian laws, but I would think that if the damage occurred in shipping, the responsibility lies with the individual or business that shipped the article. Also, it should have been insured, unless you specifically requested that it not be.
At this point I would recommend that you not open the instrument yourself, lest the seller try to claim that you caused whatever damage has occurred. Instead, take it to a competent accordion repair person (I suspect Malcolm might be able to recommend someone nearer to you than himself) for an assessment of the condition and whether it's worth restoring to good playing condition, and an estimate of the cost to do so. This could then be used in further negotiation with the seller.
Or, if you wish (sounds like you might), simply return it to the seller/sender for a full refund.
In any case, you should check with eBay regarding any protections they may provide under their rules. (Did you pay via PayPal? I think they also offer some sort of protection.)
Dear JimLucas, thank you very much for your feedback
Yes I payed using paypal, the seller said that he can't be responsible for shipment faults, still he claimed that he "will find a way to make me happy". He offered me 4 options one of them is a discount on a 48 WELTMEISTER (around 100 USD for the accordion) that is in a prefect condition . I'm a bit skeptical because the seller does not have one single negative feedback for his sold items which are all accordions . Do you guys think I should accept the deal ? I asked for a video that proves that the accordion is working 100%.
I tried contacting a local repair person and when he knew that the accordion is made in Russia he said it might be a waste of time working on it , so maybe when I contact Malcolm he will be able to help!