John--you're right. When you get right down to it, expensive as they may be, the real cost of ski lessons for many people is the time taken--or wasted. It's hard to put a price on that when you're on vacation! The industry is well aware that many vacationers, while they may be well off financially, suffer from "time poverty" (sometimes as a consequence of their financial success!) And there is no way to refund the time.
Even if you get a second lesson for free, there may be a cost involved in the first one. On the other hand, there is always SOMETHING to learn. And while you have described the scenario of not realizing how bad the lesson was until much later, I believe that quite often the reverse is also true--you may not realize the VALUE of a lesson until later! "Aha!" moments are rarely immediate--they're often the result of many ideas, feelings, and "things" gelling and gestating, and finally coming together in a wonderful moment of "Eureka"--weeks, months, or even years later!
Anyway, yes, it is customary--although not usually "official" and in writing--for ski schools to have a full satisfaction guarantee. On behalf of the whole resort, they want you to be satisfied, and will often go to more than great lengths to accomplish it. I've seen people unsatisfied with a group lesson get a "free" private lesson, usually with a top instructor hand-picked to please.
It is unfortunate that more people don't take advantage of this. I've always recommended that people go back to the ski school desk either way--to commend the ski school and instructor for a great lesson, or to "discuss" a less-than-satisfactory lesson. If more people did this--if more students were more obviously demanding of high quality and unwilling to accept anything less--ski schools would be forced to improve and deliver. While their short-term profits might diminish because of higher labor costs, I can't think of anything more likely to help the resort, and the industry as a whole, in the long run!
By the way--I should add that the willingness of the ski school to "make up" to a dissatisfied customer does depend to a great extent on the attitude of the customer. Discuss your experience in a rational, helpful, respectful way, and they are likely to bend over backward to help you. Act like a demanding, self-important dolt, and you may not get what you want. I've seen them both. It's just human nature, of course.