When I first attended a large coupon workshop, a woman in attendance turned to my friend and me and proceeded to whisper about how you could purchase a different item than a coupon intended. She had found out about decoding barcodes. Though my friend and I laughed about it later, it's really no laughing matter because these kind of shoppers hurt future deals for the rest of us.
Recently, there's been a fake coupon circulating in e-mails for a free bag of Doritos. The company has put out a warning about it, read here.
excellent post on Moms Need to Know about coupon ethics.
As for me, I'll skip on eating those Doritos, free or not.