People are declared trangshi by the verdict of the Trader Council. Mostly lone survivers, who count as the worst kind of bad luck, are made outcasts. This is supposed to ensure that the bad luck doesn't befall other Traders. Trangshi are to carry an unmarked Trader staff. Thus other Traders may recognize the trangshi and can prevent interacting with the outcast. Traders are even forbidden to interact with a trangshi as this would only bring their bad luck onto them and their family.
An alternative to making lone survivers trangshi exists in the form of cleansing their luck, giving them a new name and making them a member of another family. However, this rarely happens.
Traders consider a trangshi's bad luck as a disease.