He whose life embodies the truth is a real saint. The characteristics of a saint have been described by Sage Kapil in Kapilopakhyan, by Lord Krishna in the Bhagavad Gita and by Lord Ram in Aranya kānd of Shri Ramcharitmanas. Seekers of knowledge should read these scriptures for further guidance on this matter.
One should not try to sit in judgement over saints. In whomsoever one finds the characteristics of a saint, he is a saint. If we become true disciples, we will definitely meet a real Sadguru just as the great Guru Shukdevji went to meet the great disciple King Parikshit on his own.
Guru is one who removes darkness. He removes the veil of ignorance (darkness) with the light of his knowledge. He is a master of scriptures and a seer of truth. Such a person has not only studied the truth in the scriptures, but practises them and has experienced the Supreme Truth within his soul. He embodies the truth. Such a Guru leads a life of truth enabling others to realise that truth inherent in their own souls.