Folklore or "Fake lore"?
Some Wiccans keep a journal or track their revelations in a book. This may take the form of an actual book or something like it but, it is meant as a repository of knowledge gained during study of the esoteric arts. Manny commercial products boast the fact they are copies of, or contain portions from a book of shadows, once owned by well known celebrity Wiccans. Whatever their price each one generally contains a bland and facile coating of lifestyle marketing that tends to mark them as suspect upon closer inspection.
Folklore, spells, recipes, prayers, chants, moon cycles, compendiums of various sorts, cultural information from (ahem) a credible practitioner from that-specific-place, and more, may be crammed inside any one of these slickly minted tomes. A hand written grimoire of well plumbed and practiced wisdom, for sale at the local new-age book store, is much harder to come by however. This does not make it any less suspect however. The finder would do well to consider the source, if known, for perhaps the work should be thought of as even more dubious because of it's authorship.
No matter the source, each will contain a similar base knowledge that focuses strongly on nature in various forms, and the control of it. A farmer's almanac is not far removed from this goal except that muscle and bone, sweat and manual labor go into the land to reap a reward come harvest time. A good and worthwhile book of shadows will contain a more subtle approach toward the same or very similar goal. Spiritual muscle and mental labor will, in a more oblique fashion provide the reader hopefully with helpful guidelines of how and what to expect once the book is explored and better understood.
Sometimes such a book may be a test for the reader. These type books of shadow are sometimes written in code, which must be de-crypted before their secrets are exposed. Usually, this is very rare but, some more eclectic scribes are fueled by a paranoia about how the information may be misused by some, to bring harm intentionally. False information or disinformation is sometimes included along with the real and important portions so as to baffle the less determined or tenacious mind. This "fake lore" sometimes gains a level of credibility by being repeated and spread often enough by the unsuspecting, and irresponsible.
Some Wiccans understand how and why this happens and yet many times do not challenge it or expose such fraudulent works. Other Wiccans attempt to point out such books in private or public ways and find their efforts derided or challenged by some who insist on the authenticity, or integrity of a work. This many times allows some damage to occur to the religion since it has no central authority to vet or judge these works as worthwhile or worthless.
Once absorbed into the popular culture they take on a life of their own and the media generally adds insult to this injury. Sometimes this happens when religiously focused news that focuses on Wicca is broadcast out of context, biased, or simply filled with misconceptions predicated upon simple but understandable ignorance. A lack of of documentation or sourcing simply deepens any such mystery found within a book of shadow, and it tends to spin further out of control. Modern film has done much to bolster the image of Wicca through the release of certain big budget, well marketed films. But again, the hype and drama that brings general attention through it's lens also lacks focus on the actual reality upon which it may be loosely basing the tales that are so well told. Producers of TV and film have little time or patience to get facts right or to properly contextualize the truth of matters where Wicca is concerned. They would no doubt have a very boring show as well since, unless setting up a documentary, little research will be required before a final cut is ready for mass market distribution.
Any book of shadow worth having was written to focus the reader beyond the words or symbols on the page. These books are an example of years of a history and an experience that has been distilled into a single point of clarity when done well. Sometimes these books are intentionally designed to be simple, yet meant to confound the reader by challenging them to think more deeply. Beyond a sometimes incoherent notebook filled with scratches, there may lie a wonderful work of mystic art. It is a magical tome that may only be read and understood by a few, or even a single person. Hopefully when the proper person arrives to read this book of shadow, it will reveal it's secrets and allow wisdom to be gained. Though not always the case, it is the main purpose of the writer, and the next eventual reader.