People who know astronomy, geography and yin and yang are not outstanding in any industry. Why did they choose to be grave robbers? You know, grave robbery has been illegal since ancient times. Moreover, it is immoral to dig people's ancestral graves, and the clan concept of China people is even more serious. It has always been dismissive of such immoral behavior.
People used to call grave robbers "local tyrants". These people often have no education and skills, so they have to choose to be grave robbers in a society where there was no way before. After all, you can't steal the living, only the dead.
And most grave robbers actually have no technical content. Their job is to dig a stolen hole outside the tomb, then climb in along the stolen hole and steal the funerary objects. After entering the modern society, with chemicals such as explosives, grave robbers' methods of robbing tombs are more rude. They often directly blast the ancient tombs and then steal all the valuable funerary objects inside. Because of their destruction, these will often become irreparable losses in the archaeological community.
As for the saying that grave robbers know astronomy and geography and Yin and Yang, it is probably because they read many novels such as grave robbery notes. I can only know a little at best. After all, after decades of work, the more you work, the more skilled you become.
Moreover, many ancient books and documents in China are open to the outside world, and the famous figures in the history of China have recorded their native place, life and official position. Ordinary people may also infer their burial place after death through the investigation of historical materials, not to mention those grave robbers.
Therefore, grave robbers are not as evil as you think. If they were really that good, they wouldn't be grave robbers.