This is a story with a moral: owners of brick and mortar book stores, especially brick and mortar used book stores, are heroes.
I concur.
Actually, Cliff Janeway, main character and narrator of this series and owner of a used book store, never lets readers forget he is heroic. In fact, Janeway portrays himself as being Trustworthy, Loyal, Helpful, Friendly, Courteous, Kind, Obedient, Cheerful, Thrifty, Brave, Clean, and Reverent. Well, maybe not reverent and definitely not obedient. But he lets us know that he is a splendid fellow, who is also irresistible to women.
I don't think that this is a particularly good mystery purely as a mystery. The "whodunit" aspect of the book is not nearly as interesting as the "whydhedoit" aspect, and that in turn is nothing like as interesting as the material about books, which is fascinating.
Much of the book is about a small publishing firm that produced nothing but fine limited-edition volumes. There is a lot of attention given to a spelling error in one book. In a time when many books seem to have at least one error on every page, that kind of attention to detail is certainly praiseworthy. But there is also a lot of attention to the concept of a book as a work of art in itself. Fonts, bindings, layouts are all made as near perfect as possible.
As with all the books in this series, there is also much discussion of what makes particular books valuable and how knowledgeable a successful bookseller should be.
And another moral of this story: collectors are crazy. But I suspect that a lot of people spending time at Goodreads already know that.