El Maximo writes:

Mostly, they find their instructor is incompetent long before they spend
years studying.

Many instructors are incompetent, but many students lack motivation as well.
Either may prevent a student from gaining competence in a language, even after
many years of study. And there are other factors.

Incompetant people can claim to teach it without any of their students
actually learning anything.

Yes. And students can claim to study it without actually learning anything as
well.

Fortunately, unless the teacher impersonater is
exceedingly stupid, they realize that they're not making the same amount of
money as the real teachers and find something else to do.

Many of the worst teachers have impeccable credentials and are well paid, and
vice versa.

I don't doubt it. I suspect there are no real standards one must meet in
order to claim to be an english teacher in France.

Read _Sorbonne Confidential_.