Judging a book by its covers

A 10th-century treasure binding of a Gospel Book, Paris, Bibliothèque nationale de France, Latin 9393

Don't judge a book by its covers, they say. The inside is what counts, they say. The advertising community is not so sure. The cover design is said to increase the marketability of a book by 50%, by a conservative estimate, and by as much as 80% in some …