The only lesson I've ever had was bought for me in 73,1st time on skis. I could never afford it. I've gotten and given a couple impromtu lessons for only tips. If your going under the table do it under the table. It's probably someone who cant afford $100 an hour any way. as far as hardboot lessons they don't exist, If I got paid to teach someone to snow board in '88 I sure wasn't taking away from the area as snowboard instructors didn't exist. Consider it a tip and don't ask don't tell.
Advertising is one thing but if they seek you out it's an exchange between friends, no dilema.