It might be argued that Sư Vãi Bán Khoai or Potato-Selling Monk was a part of the peasant masses and acted in their midst. During his evangelizing missions, he typically camouflaged himself as a small vendor selling potatoes in order to avoid the scrutiny of the French police. This is how his nickname emerged. Potato-Selling Monk also disguised himself as a nun therefore Vãi, the title of a nun, appeared in his nickname. Although he was also known as Mỹ, his full lay name, as well as the birthplace and the facts of his life, are still unknown, as no documentary records with reference to Sư Vãi Bán Khoai remain.
Potato-Selling Monk manifested himself when Bửu Sơn Kỳ Hương movement was forced to scale down its evangelizing and social activities mainly due to French oppression. In order to deliver his message without being subjected to detention, he was forced to use the disguises of a small vendor or even a madman. Potato-Selling Monk mainly operated in the area of Vĩnh Tế Canal, where he preached the Bửu Sơn Kỳ Hương doctrines. He started his evangelizing mission in 1901 but had to retreat into obscurity shortly afterwards, nearly only one year after his advent. Despite all his camouflage efforts, he became subject to police scrutiny anyway.
Although his evangelizing career did not last long, Potato-Selling Monk compiled the Laymans Prophecies, or Sấm Giảng Người Đời, including eleven chapters or small booklets of verses. In his writings, he highlighted the millenarian concept of the Three Eras, or Tam Ngươn. On the other hand, the Laymans Prophecies represented a sort of sophisticated amalgamation of religious and patriotic values. The Laymans Prophecies have been viewed as Potato-Selling Monks major contribution to the development of Bửu Sơn Kỳ Hương ideology.