I'd say look at the teacher's students. Do you want to be like them? If you see a good and harmonious sangha, and if they're practicing well and are good people with good hearts, then you have a cause for trust.
Tenzin PalmoWe live in a society which is heading in one direction, so it's good to have at least a few friends who share the same values and can encourage us and help us to remember that we're not alone or peculiar, but that what we're doing is a very valid way of life. This will encourage us to put the Dharma at the centre of our life and not the periphery, to use our daily life as our Dharma practice.
Tenzin Palmo