Bullshit. Unless you can point to real evidence this is true, you're just guessing.
What? How do you think that coupons actually work, anyway?
1) You present a coupon, and you pay less cash at the point of sale than you otherwise would have. This is not a mystery. It's the whole point. If it's the retailer's own coupon, then they are basically putting the item on sale in exchange for having a trackable form of marketing. If it's a manufacturer's coupon, then the retailer is participating in a mechanism wherein the manufacturer and retailer have worked out a back-channel compensation scheme for the retailer having collected less cash during the transaction. This is also not a mystery.
2) When you present the retailer with a bogus retailer coupon, you're getting a discount that's disconnected from one of the key reasons they issued the coupon in the first place: to understand which marketing methods are the most constructive. When you present the retailer with a bogus manufacturer's coupon, one of two things happens: the retailer eats the loss, or the manufacturer does. Again, why are you acting like this is some strange unknown? Or, are you just hoping that someone there's a third magical possibility that makes it just fine to rip off businesses with fake coupons? Yeah, I thought so.