In the Eleventh Canto of Śrīmad-Bhāgavatam, Third Chapter, verse 21, Prabuddha tells Mahārāja Nimi, "My dear King, please know for certain that in the material world there is no happiness. It is simply a mistake to think that there is happiness here, because this place is full of nothing but miserable conditions. Any person who is seriously desirous of achieving real happiness must seek out a bona fide spiritual master and take shelter of him by initiation. The qualification of a spiritual master is that he must have realized the conclusion of the scriptures by deliberation and arguments and thus be able to convince others of these conclusions. Such great personalities who have taken shelter of the Supreme Godhead, leaving aside all material considerations, are to be understood as bona fide spiritual masters. Everyone should try to find such a bona fide spiritual master in order to fulfill his mission of life, which is to transfer himself to the plane of spiritual bliss."
The purport is that one should not accept as a spiritual master someone who is fool number one, who has no direction according to the scriptural injunctions, whose character is doubtful, who does not follow the principles of devotional service, or who has not conquered the influence of the six sense-gratifying agents. The six agents of sense gratification are the tongue, the genitals, the belly, anger, the mind and words. Anyone who has practiced controlling these six is permitted to make disciples all over the world. To accept such a spiritual master is the crucial point for advancement in spiritual life. One who is fortunate enough to come under the shelter of a bona fide spiritual master is sure to traverse the path of spiritual salvation without any doubt.