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 PalmoTo want not to want, you'll tie yourself in knots. So this is why the Tibetans always say, just relax the mind and open.
Tenzin Palmo