Bah, saw this article the other week, sorry to be so opinionated but I think it's sheer rubbish and feel sorry for anyone foolish enough to purchase.
Some of my favorite quotes:
"The lithographs are primarily unsigned. As Mr. Moors explained, unsigned works eliminate the potential problem of forged signatures."
"Galleries will sometimes take sizable markups on works of art they purchase for resale, according to dealers. By contrast, Mr. Moors said, Costco is charging a maximum of 14 percent over what they pay him, the same markup it applies to all its merchandise."