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 PalmoWhen I look back I can think that of course I've been lazy and haven't practiced as much as I could have and have wasted time. Still though, I look back on my life and I think that really, I am very happy that I lived my life the way I have and I would never ever have wished it any other way - especially, the six years with my lama and then the 18 in Lahul.
Tenzin Palmo