This question already has an answer here:
In the first book of the Harry Potter series we are told that Harry has piles of galleons inside his vault at Gringotts. Why didn't Harry draw a few gold coins from his safe and sold them in the muggle world to earn some money? That way he could've improved his quality of life in the muggle world quite a bit
I know the subject has been approached in other questions, but the closest answer I got was what would happen if Harry bought silver in the muggle world and sold it for gold in the magic world. I want to know what would happen exactly in this case.