One exemplary thing about BJJ is the belt system. Simply no kid blackbelts at all until they are 16 or 18 depending on the instructor. That in and of itself does a lot to maintain quality!
QFT!!! And this is one of the many things I like about BJJ!!! I could only wish other arts would follow these principles. Funny....people cry and moan if they walk into a TKD school and dont get a BB after 2yrs, but people seem to be perfectly cool with the fact that they could wait 10 or so years before reaching BB in BJJ.