Were these "!textbooks" on Pinyin and the marking of tones by numbers?
Must have been a ground-breaking "work" and a major "achievement" for fools who love to read nonsense. Hopefully, they sell quite well......

My books deal with contemporary French philosophy. They sell well given the field. But the profit margin is low.

I didn't do them to earn money. Is that why you wrote yours?

Sounds rather mercenary for such a "dedicated" teacher.