A famous Feng Shui master Kwan Fung Cheung (Cantonese) 關鳳翔 published an excellent book in 1971: The Principles of Kan Yu 堪輿學原理. In my opinion, it is the best Feng Shui book ever written. Here I will summarize the last section of Chapter 3 in this book.
The author categorized five types of fake Feng Shui books as follows:
 Someone discovered truth about Feng Shui and believed that his ideas were better than those of his predecessors. However, since he was just an unknown small potato, no one would pay much attention to his discovery. Therefore, he published his book under the name of a famous Feng Shui master. Examples are (1) Challenging the Dragon Classic 撼龍經 (2) Suspecting the Dragon 疑龍經 (3) Song of Formulation Leaking Heaven’s Way 天機入式歌 (4) The Precise Theory of Spiritual Castle 靈城精義. These are all valuable Feng Shui books but the authors were people who did not have a big name. Therefore, famous people were used to name the authors of the books. (1) and (2) were assigned to Yang Yun Song 楊筠松. (3) was assigned to Liao Yu 廖瑀. (4) was assigned to He Ling Tong 何令通.
 A good book was written by an anonymous author. Some nosey parker assigned the name of a famous master to be the author of the book. For example, Guo Pu 郭璞 was assigned to be the author of the celebrated Burial Book 葬書.
 Classic of the Green Bag 青囊經 was non-existent meaning there was no such book at all. In the Burial Book, this sentence appears 15 times: The Classic says, “……”. There was a fake book written after the Tang Dynasty by an unknown author. It was assigned the title Burial Classic 葬經 with author Qing Wu Zi 青烏子. The title of the book was later changed to Classic of the Green Bag 青囊經.
 Some very good books were written by scholars. However, they had a much higher social ranking than Feng Shui masters. They were ashamed of disclosing the fact that they were good in this art. Therefore, they employed the name of Feng Shui masters who lived generations before to be the authors of the books. For example, Snow Heart Song 雪心賦 is such a book.
 Some books were written in unintelligible language because the author was an uneducated person. An example of this type is Heaven Jade Classic 天玉經. It was a book written by some follower of the Daoist Religion. The structure and style of writing can be described best as gibberish. It was taken as concealing secrets of Feng Shui as the terms like Xuan Kong and Aixing can be found in the book. However, this book has nothing to do with Feng Shui of graves or houses at all. Later, charlatans used this book to teach whatever they wanted in different ways. They all claimed to have the uniquely passed down secrets with weird annotations.
It must be noted that what Master Kwan listed are only the more obvious fake books. Feng Shui is actually a very rigorous subject based on observation and logical deduction. The only thing that prevents Feng Shui from becoming a science is the Man part of Cosmic Trinity because two different persons can react differently to the same qi.
If anyone sells you courses with wild claims of lineage, just forget it.