I think you're doing a discredit to photography tutors and courses, they're not spammers. I accept the point that it could become cluttered, but I think that could be quite easily managed with the same heading hierarchy the site uses now.
If a private person/company chooses to advertise they'd be subject to some basic rules.
The thing I'd like to see is a sort of safeguard for consumers - when I go googling for courses, I've got nothing but biased testimonials and website quality to base my opinion on.
Anyway, I think I've lost this one, there's a lack of interest haha!