At some point, what CAN you do? Not much. Even an instructor recommended word-of-mouth WON'T necessarily be right for you. Maybe, but no guarantee. Same the other way; an instructor someone trashes might've been just your cup of tea. You HAVE to (IMHO) accept that the hit-and-miss of it is there. Unless you've seen the instructor at work, or had a previous lesson, how can you possibly know?
I think it's mostly preparing yourself - I happen to agree very strongly that a ski lesson's success or failure gets back to the student as much as the instructor, if not more so - for a lesson that might not be at all what you expect. And it's good that you'll be specific with the ski school/instructor about what you want to work on. (But, for example, your preparation should include knowing that you might very well want to work on short turns, just to have an instructor say "sure, let's go do it," then, after watching you make a few turns, suggest "we go back a step" to iron out some small detail he/she sees that need addressing before going to the (obvious) short turn work.
That instance alone is probably enough to get some people to cry Bad Lesson. When really maybe they missed the opportunity - if they just went through the motions, marked mainly by passivity - to do some "detail work" that, while not seeming to, correlated directly with the dynamics of the short turn. For example.
Besides all this, even if you DO end up in a truly bad lesson - and you know it - it's still on you to first get
SOMEthing out of it (figure out how/why it's "bad," for one), then discuss with the ski school (as constructively as possible).
I've had three lessons. My first two ski days a few years ago and another last December. The instructors (all men) were three very different individuals, with dissimilar styles. Two of the lessons were great, the other, poor (mainly attitude/laziness). (Again, though, early in the lesson I realized the non-fit, decided to make the best of it by at least paying attention, while not getting bent out of shape by the attitude, and working at the fundamentals I'd been introduced to the day before.)
Anyway, to reiterate, the more responsibility you accept for your lesson, the better the chance it will be successful.