I use retailmenot before I buy anything, even pizza there's coupon codes.
It works because you click the link to apply the coupon and a very large majority of these sites they are affiliates and thus get a commission.
It is user generated, they don't actually find coupons, anyone can submit and then people can vote them as good or expired.
Its a good business model but I highly doubt that someone with your questions will be able to rank for even many of the smaller online stores, the whole first page of google for terms like "store coupon code" are dominated by the really big guys and there are hundreds more that will never see the odd click.