Gu Rou Chen makes a sound observation. High level instructors, at least in our system, leave the teaching of beginners to junior instructors as a matter of course. My Sifu simply doesn't teach beginners, and I only very rarely work with them anymore.
In regards to the issue Audi raises of whether or not an instructor may see a question of lineage as a slight or a challenge, an instructor to whom lineage is important will almost always publish it up front, thus avoiding chances for misunderstanding. Also, as above, junior instructors tend to be more "conversational" and the approach to such subjects as lineage can be less formal with them than with the head instructor.
Lineage isn't the only test, to be sure. Do they train martially at senior level? The cost of classes is an important issue, too, and not just for tightwads!
There are also intangibles such as how the school "feels," how the students look, etc. Of course, these are mostly things which I learned to appreciate only after I had studied for a few years...
Ultimately, I believe that it comes down to the fate that one has earned in this lifetime through personal development and evolution. Those fated to study with the Yang family will study with the Yang family because of the "golden opportunity" of a happy coincidence of location (or perhaps moving to a city in which the Yangs teach)and the fact that only that level of expertise will satisfy them. Those fated to study with Sunfrog down at the health food store will study with Sunfrog because that level of expertise will satisfy them, and that is where they'll choose to stay.
[This message has been edited by Polaris (edited 08-06-2004).]