How can laypeople recognize a true Buddhist practitioner or master, whom they may trust and learn from?
According to Most Venerable Thích Thanh Từ, the following three criteria may be used:
1. Does that person observe the precepts s/he vowed to take?
2. Does that person understand the Buddha's teachings (Buddhist Dharma) correctly?
3. Does that person actually practice what the Buddha's taught?
The person may not have a wide knowledge, and may not know everything in Buddhist Dharma yet, but the first and the third criteria are important and must be met.
Source:
From a Dharma talk by Most Venerable Thích Thanh Từ in the USA in 1994.