Basically, an accrediting body, right?
I agree, but I don't ever see this happening. Not only will ineffective martial art schools not seek accreditation, but many schools that teach martial arts that are effective probably won't seek it either (due to *insert philosophical babble here*), which would effectively make the ineffective martial arts indistinguishable.
While some styles do have an accrediting body (in fact, it's national and international governance is a requirement for any olympic sport), it's helpful but not essential.
BJJ, as an example, has a pretty reliable ranking structure. Progression is predictable and based on a combination of performance and technical expertise. TKD has this, too. So does Judo. Wrestling, Kyokushin Karate, Sambo, fencing, Savatte, Western Boxing, San Shou...
It's how two people who have never met, who train with people who have never met, from hundreds or even thousands of miles away, can show up to a tournament on a Saturday morning and compete on a level playing field. Without some objective standards for performance and expertise, people would get murdered all the time. It would be unsafe.
But somehow, on local, regional, national, and international scales, this happens all the time. For some styles. Not all. Not Aikido. I just can't put my finger on the common denominator... I guess it's a mystery we'll never solve.
In Aikido, a guy can show up and it's an utter crap shoot.