Qing Nang Xu 青囊序 says:
Please examine the ancient graves handled by the same Feng Shui school.
Among ten graves, nine yield poverty.
Only one grave generates prosperity.
The incoming mountain and outgoing water are appropriately loving.
* 一家 can mean "one family" or "one school (of thought)".
**合情 can mean "correct according to situation". When it is used in Feng Shui, it means that the yin and yang, mountain and water, are correctly (lovingly) located.
The author of Qing Nang Xu is Ceng Wen Chan 曾文辿, the most important disciple of Yang Yun Song 楊筠松. In these lines there is embedded one secret that most Feng Shui masters overlooked and overlook.
The "one school" does not specify which school. It actually refers to all schools.
If you examine the ancient graves handled by any Feng Shui school, you will find that nine out of ten have poor descendants because the mountain and water are not appropriately located. Only one grave has prosperous descendants because the water and mountain are well matching. Why?
We must not overlook the word "ancient" in the context. We must not forget that the magnetic field of the earth is changing. Even if an ancient grave was handled correctly to have the mountain and water matching in the best way when the person was buried, after a hundred years the change of the earth's magnetism has caused the mountain and water directions to be inappropriate today. It will be fruitless to examine ancient graves to verify the correctness of a Feng Shui formula.
Furthermore, yin zhai 陰宅 feng shui is only one small part of life. It may be the body (體) but the application (用) is yang zhai 陽宅 feng shui.
Using ancient graves or ancient buildings to verify the correctness or incorrectness of a Feng Shui formula is simply an invalid approach. It may actually point to the otherwise.