Why doesn't the huge difference between the muggle and wizard gold exchange rates lead to the collapse of the wizard economy?
We know, that 17 silver Sickles is worth a golden Galleon. However, in the muggle world, you can get more than 50 kg silver for one kg of gold.
Even if Sickles were the same size as Galleons (if I remember correctly, they are much smaller), and the gold content of Galleons was the same or even less than typical muggle gold coins, it would still be highly profitable, to buy silver in the muggle market, exchange it for gold in the wizard market, and sell the gold in the muggle market.
How is it that no one does it? It could ruin the wizarding economy in a very short time, or at least draining most the gold out of it and altering the exchange rates between Galleon and Sickle?
We all know that magic can't create money or precious metals...