This is confirmed in Śrīmad-Bhāgavatam, when Nārada speaks of the different symptoms characterizing the four divisions of social life. Nārada therein states that brāhmaṇas, kṣatriyas, vaiśyas and śūdras should be selected by their individual qualifications. In his commentary, Śrīdhara Svāmī has noted that birth in a family of brāhmaṇas does not necessarily mean that one is a brāhmaṇa. One must be qualified with a brāhmaṇa's symptoms, which are described in the śāstras. In the disciplic succession of the Gauḍīya Vaiṣṇava sampradāya, there are two great ācāryas (Ṭhākura Narottama and Śyāmānanda Gosvāmī) who were not born in brāhmaṇa families but were accepted as spiritual masters by many famous brāhmaṇas, including Gaṅgānārāyaṇa and Rāmakṛṣṇa.
In this way there are symptoms which both the prospective spiritual master and the prospective disciple must have, and both the disciple and the spiritual master must see whether the other is eligible to become either a bona fide spiritual master or a bona fide student. One should then know that the only worshipable object is the Supreme Personality of Godhead, and one should learn the various mantras and sacred songs.