Well, you'd have to look at the standard within the association/federation. If the instructor is unaffiliated, then he got his training from somewhere. Korean striking art + hapkido culled joint locks is not in any way, shape or form hapkido. If the instructor is actually teaching hapkido, he should be happy to share his lineage. If you go back far enough in his or her lineage, then their hapkido comes from an established line, which will then give you some basis for comparison.So since there is not standard to compare to as correct Hapkido, and there is no combat contest to compare who develops the best fighters, it seems that I would simply pick a teacher that impressed me the most, that I felt was a good fit for me and that there is no way of ever knowing how good one Hapkido teacher, or student is compared to another. If I were recommended to a specific teacher, it would simply be based on the opinion of the recommender, not on any type of fact of ability, or achievement? So it is really a person's personal taste?
Hapkido is a young art, so many of the pioneers are still alive and practicing. You certainly are familiar with that within the context of taekwondo. It isn't a big mystery as to who learned from who and where they fit in in the grand scheme of hapkido. If they cannot trace their line back to Choi Dojunim, then it probably isn't hapkido.
There are other factors in school recommendations that are more related to the quality of the school owner, whether or not they might be a good fit for a specific customer, and less to what art they are teaching.