Secretive and fraudulent do not need to go together.So are closed door systems, in fact I'd say they are better at making people feel they are learning something super.
As for the schools, you asked for examples, would you prefer I list schools that you've not heard of? Don't see what good that would do to be honest. Point is the same, a good instructor can teach good material and make a living doing so. Takes a combination of not just teaching, but also business skills.
This commercial vs "secret" is a faulty split, but if that's what you are after check out the back of a martial arts magazine. "Secret style only I know because I awas the only one worthy and learnt it in a secret room with no witnesses" is a fairly widely used marketing scheme, usually associated with frauds.
Sean