For example, Cathy Gallagher's Secret Lover Collection of greeting cards offers a Christmas card that reads, "As we each celebrate with our families, I will be thinking of you," the Baltimore Sun reports.
Gallagher, of Bethesda, Md., says she expects hot sales since so many married people have affairs.
But, the Sun reports, some retailers won't carry the cards out of fear of alienating customers, while others say their customers would be too ashamed to buy them.
Despite the naysayers, however, Gallagher says her business is off to a good start as she fills orders across the country.
Gallagher says she does not condone affairs and simply saw an untapped market. And the mother of two and wife for 15 years says she has no intention of ever using her own product.
"You don't have to be a murderer to write a murder mystery," she says.