How can one recognize the human incarnation of the Lord?A.
The real characteristics of the Lord as declared by the Veda are the special knowledge (prajnana), the love (rasa or prema) and the bliss (ananda). The Veda also says that one must ascertain whether the person who, one thinks is the human incarnation, possesses these three characteristics. The characteristic property of the fire is heat. Any person who is near the fire should experience the heat and then only we can say that the fire is hot. Similarly the Lord in human form must make others experience the jnanam, prema and ananda. The Veda says 'Esha Hyeva Anandayati', which means that He creates Bliss in the hearts of others.
The Lord cannot be recognized merely by the miracles He performs because even demons can perform miracles. Miracles are only associated properties like jewels on a person. They are not characteristic properties. Moreover the Lord in human form always avoids performing miracles unless there is an emergency. The reason for this is that in case of the human incarnation of the Lord, He dwells in the human form, which is a product of nature (prakriti). Therefore the Lord abides by the rules of the nature.
These rules were formulated by Himself. No administrator likes to violate his own rules. Even in emergency situations, when He violates the rules of the nature, He keeps the violation a secret to avoid setting a bad example to others. When the administrator violates his own rule due to some unavoidable situation or for the benefit of some deserving person, he will be discreet about it. He will not publicize the violation.
Only demons violate the rules of the nature without hesitation. They are also the ones who are interested in advertising to the world that they are powerful and that they can break the rules of nature. They bother neither about the violations of nature's rules nor about setting a bad example to others. They neither formulated those rules nor are they interested in the well-being of people.
Source - http://www.universal-spirituality.org/qanda.html