I did a speed reading course in high school and often wondered if it was a scam.

Not a scam, scam more a motivational speaker/Eat less exercise more style scam. If you followed it through it would work but almost no one follows through hence the course/advice becomes bunk.

For instance one thing we were taught was to first skim the book/chapter really quick then read it 'properly'

Makes sense to me, but I never do it.

People do have different reading speed levels and I don't think it's all innate so I don't think it a crap idea.

I would agree that maybe the teaching is currently more based around customers and less about pedagogy though.