Commission rates in the airline industry range from 0% to 15% depending on distribution channel, POS, class of service, fare class, the existence of any agreements with the airline...That being said, most fares earn minimal or no commission (full fare and premium fare tickets generally still do), and sites such as expedia generate most of their profits from hotel bookings and package vacations.

As long as the % of GCs which go unredeemed exceeds the discount given, the deal would still work in AC's favour due to the GCs effectively being interest-free loans.

But beyond that AC could actually benefit from various other factors such as an decrease in commission payments, a shift to direct sales and "locking in" unloyal/flexible customers (e.g. AC selling GCs to students at a 20% discount during the first week of Sept. only - combined with a small "we care about students" marketing campaign - would likely result in thousands of students buying GCs and being "stuck" with flying AC 3, 6, 9 months later, thereby eliminating the option to fly another airline).