I have no answer to that except to say they must be blind in some artistic sense. I too have come across this many times. Because of this, when I first visited Japan 25 years ago I visited many places before choosing where to train. I am now back in Japan again - as of last week - searching.
I have been involved in various sports (plus coaching) since a young age and have always followed the skill.
I think your wide background, and your insistence on seeking the "real thing" outside your immediate lineage, educated you to some extent in terms of perceived quality. You are surely rare in this respect.
During the course of my aikido career, I have seen groups - in some instances, whole organisations - whose aikido has certain good points, but who have poor posture and (in my opinion, at least) lazy, sloppy and complacent technique. The teachers set themselves up as transmitting the "authentic" art, and their students, in the absence of much to compare with, believe them and copy their bad habits faithfully.
With regard to the original thread topic, I don't think there is any absolute guarantee of quality, regardless of paper qualifications. As Philip said, the moderation of dan gradings by shihan from the respective Hombu gives at least some assurance of a minimum standard, but then we get back to the thorny problem of a good practitioner not necessarily being a good teacher.
I would always say do some research online ("Google is your friend") and then, bearing that in mind, go with whichever group you like most on an intuitive level.