Yeah, that's one of the flaws with it being a "numbers go down" type game is that it makes percentage coupons and the like much easier to "cheese". For the demo were working on we have instead opted to go for a "numbers go up" version instead (where you add *to* the cart to hit the total instead of decrementing the cart that makes the total). Hopefully it will be a much more fun experience for people! :)
Thanks so much for playing!!