It seems improbable that the booming school equipment business of Diagon Alley survives on one school's worth of customers, especially if most of them only shop once a year.
It didn't seem to me there were so much school equipment business. If you look at the shops Harry went to the first year, it's a dress shop, a book shop, a wand shop, a potion ingredient shop, a broomstick shop, a pet shop, ... none of them sound dedicated to school equipment. They probably have a lot of school equipment in stock/display during august, like supermarkets do here too, but continue selling their goods to adult wizards the rest of the time.
The rest of your objections do hold, but I just fold it into "canon HP isn't very consistent" suspension of disbelief... of course, it makes things tougher for EY when he's making a consistent version of it. But that's part of what makes HPMOR funny/interesting.
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: