There are obviously exceptions but in a majority of cases, the bound books produced by companies such as A+, warringul etc are going to be better than the ones produced by students. Sure his bound book may be "very good notes" and suited for him but not necessarily everyone. The ones created by the company would generally cover everything and leave space for students to personalise it for their own needs.
I don't take business management so I can't say much about your notes but I've read Mao's ones. A lot of it isn't for specialist and lots of examples look like text-book cut outs anyway, so I wouldn't say it's "better" than a "professionally produced bound book" ( although i'm not saying it's worse)
I would also bet that if you were to ask 1000 different students that if they had to buy a bound reference, would they buy it off a company or off a student who claims that they're good, the vast majority would go with the 1st.
Although I'm guessing here, I would bet that if there was an equivalent VCE forum to this elsewhere and a new member who got 30 for a subject posts a set of notes out there, most people probably wouldn't even look at it, less consider it to be better than other options. Basically, I'm saying that having gotten a 50 alone would make a lot of people refer/use the notes regardless of whether it is actually better than some other bound books. However, if he "did" get a score like the 50 you got in BM, then I would say people would buy it, thinking it would help them.
Another thing I would say is, no one is going to buy a bound book with just the seller praising their own product without any examples or reason to believe that it is going to be useful ( and not to mention, it is also more expensive than most options)