Past its shelf date

I have purchased a book in an airport bookstore. An act that by itself does not merit a mention.
But now, after a closer look at the cover, I have found something remarkable: there are words on a cover (not a sticker the bookstores or publisher sometimes put, but really an imprint on the cover) that announce the following:

GREAT READ
GUARANTEED
OFFER ENDS MAY 1, 2005

(I have done my best to convey the sizing and coloring of the text.)

Now I am confused and concerned. Have I bought a book past its prime? Could it hurt me physically or mentally? Why hadn't the seller warned me on the possible dangers of that purchase? Should I sue?

The book, accidentally, is Bad Business by Robert B. Parker.