According to the text, how can one distinguish between a mere teacher and a genuine Sadguru?

Chapter 48 of the Sai Satcharitra provides a clear distinction between a mere teacher and a genuine Sadguru. The chapter explains that many can be called gurus—those who study the Vedas, control their breath, or give sweet talks about Brahman—but they are not necessarily Sadgurus. A key difference highlighted is the presence of direct self-experience. A teacher might have vast verbal knowledge and offer mantras, but their knowledge is "verbally hollow" without personal realization. As Chapter 48 clarifies, a true Sadguru is one who has direct, full experience and has the authority to enlighten disciples with that experiential knowledge, not just theoretical principles.