The person who had stopped Da Mao was the leader of the security team in charge of the field area. He was a famous person in the local sphere.
Obviously, he had already learned about the legends surrounding Da Mao and knew about his talent and capability in stone gambling.
Compared to a casino, the stone gambling fields and areas were more open-minded. They welcomed capable experts to come forth and gamble on the stones. That was because the fields and field areas needed a reference for the crowd. They were unafraid of someone making big money but were wary of everyone losing their bet. If that happened, they would gain a bad reputation and no one would go there to buy stones anymore.