This usually requires that the person holding the patent provide enough trade to satisfy demand. Otherwise the pressure to create a black market is irresistible. So trade could be restricted to a few powerful wizards - perhaps to each wizarding government - but it could not be eliminated entirely.
And since wizards can provide extremely valuable services to Muggles in trade, they would capture almost all the Muggle gold in return. Then we would observe wizarding billionaires, making fortunes of a 100,000 Galleons negligible in comparison. That we don't observe this is strong evidence that trade either doesn't exist at all or is universal and unrestricted. Since the story offers ample proof that trade isn't universal, it must be nonexistent. But it's not clear what is preventing trade.
Wizarding culture. Trade with muggles was basically worthless until a single wizard's lifetime ago, so the prejudice hasn't had time to evolve away yet.
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 97. The previous thread is at nearly 500 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system.
Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: