Credit shopping is nothing new. I did it when I was in high school many many years ago. I took my English OAC in a public school in summer because the English teacher in my school is really though. Buying the credit without studying is a bit too much, but it is natural that students will take the difficult courses with an easy teacher. For example, I got a 20% grade increase. That makes a huge difference in university application. The only fair admission system is public exam system like HKCEE.