Still contemplating sending a modified version of that rant about the shitty instructor to the Coop GM. Not sure what purpose it would serve. The last thing I want is for someone to lose their job. Not that they would can him over one complaint. Then again, if they have had others maybe he deserves to be canned?
I would. Only because it may benefit others in the future. The instructor might just be so comfortable in his position and slacking a bit. Consider someone brand new - without any research, etc of snowboarding - gets a lesson from this guy and either calls it quits on snowboarding forever or learns something an incorrect way. His shitty instruction serves no one.
Mention in the letter that you don't intend for him to lose his job, but that it did make you debate returning to the hill for another lesson. Revenue matters to businesses, as (should) quality service. Besides, you spent good money on something that didn't meet your expectations.
I'm in a sort of service related business. I'd MUCH rather know that my clients are satisfied, or even if they're not. Constructive criticism makes me better at what I do, keeps me sharp, etc, which brings exposure to new clients. It's a win/win.