In defence of the school, many people ring up with 1 day to go for their flight which makes it hard. They also come in 2 years later hoping that it is still valid.
Gift certificates are an interesting beast too.
I knew of a company that once did Joy Flights and sold most of their tickets on-line or over the phone. At least 40% of the gift certificates if not more were never redeemed.
You could park an un-airworthy TigerMoth or similar next to a road, advertise Joy Flights (or Adventure flights or whatever), offer full refunds to those that try to book and over 40% of your purchasers will never show.
A little deceptive, but food for thought!