Hi all .. first time poster here and just lurking around the world of stacking. But I saw this thread and it sucks to see a business get screwed by the Govt, no matter the circumstance, especially as it sounds the business was well respected.
But just an idea .. If the basic problem is that the ATO is being a lot more "strict" in the scope of how they determine whether a precious metal product is GST exempt or not .. And then wanting to charge GST on the whole lot. well..
Would/could it be possible to alter the process, on paper? Or the "workflow" of the transaction. For example. What if you "sold" a customer raw silver bullion, which is completely and appropriately tax exempt. And then, as a service (separate to the material cost), you take that metal and then work it into a minted coin or whatever else it may be. So for a coin, you would maybe charge, a few dollars, or whatever it cost, to produce that final product, turning some cast bullion (GST exempt) into a nice minted coin (otherwise subject to GST). And then you charge GST just on the latter process. Exactly what it is - a service (Assuming you are doing this anyway, making your own line of coins and not reselling those from another mint). Effectively just splitting the coins or whathaveyou across 2 line items on an invoice, or even 2 invoices. This way, there is GST still there, but it's much more insignificant as it's calculated off a fraction of the cost.
It wouldn't really be any different if a customer supplied their own metal, and all you did was work other people's materials that they provided, and you never actually sold them the metal to begin with. You couldn't charge tax for a material your customer supplied to you. There would be no transaction for that to apply tax to. You just invoice for the work you do.
I mean .. if you had your car serviced, you pay GST on the parts and labour, not the value of the car. If a plumber fixes a broken tap, you pay GST on the parts and labour, not the value of your land and house. And so on.
Of course, there could be some BS Govt red tape that would make this unfeasible, so maybe someone can rightfully shoot this idea down, but as said, just an idea.