The books make it clear that they offer the reverse service (see the following question: What Do the Gringotts Goblins Do With Muggle Money? ). According to the canonical answer to that question, Q: When people trade in Muggle money for Wizard money, what does Gringotts do with the Muggle money? JKR: Those goblins are sneaky people. They manage to put the Muggle money back into circulation. They are like "fences" --British slang, do you understand it? ( src: America Online chat with JKR transcript, AOL.com, 19 October 2000 ) The answer also makes reference to a comment by Dharini Chandrasekaran: Just speculation, but squibs who go out into the muggle world to work will need Muggle money and also wizards might need it while doing Muggle studies research or trying to remain under cover, so I guess they keep it for reverse exchange. This seems entirely reasonable speculation. Nevertheless, I don't recall any example in the books of converting Galleons to British pounds or ot...