Unless one is omniscient or at least enjoys some degree of clairvoyance, no one can judge others. One can see how others appear and how they are behaving, but not who they are or why they are behaving in a particular manner. For example, enlightened ones such as buddhas, bodhisattvas, and sages appear in peaceful forms and wrathful forms, but all their activities will be for serving others with love. As for false tulkus, even if they show impressive performances, their goal could be for material and emotional satisfaction for themselves or their loved ones. This is why the fully enlightened Buddha said, “Apart from myself and those like me, no one can judge another person.” So, I myself have no way of judging if someone is a real tulku or not. I am only repeating what the masters of the past have said.
Excepted from: Incarnation, The History and Mysticism of the Tulku Tradition of Tibet, Tulku Thondup, Shambhala Publications