mayavadis & karmi's can't be

 
An impersonalist can become a qualified brāhmaṇa, but he cannot become a spiritual master unless and until he is promoted to the stage of a Vaiṣṇava, or a devotee of the Personality of Godhead.
A real brahmana is the natural teacher or spiritual master. Unless one has Vedic knowledge, one cannot become a spiritual master. The perfect knowledge of the Vedas is to know the Lord, the Personality of Godhead, and that is the end of Vedic knowledge, or Vedanta. One who is situated in the impersonal Brahman and has no information of the Supreme Personality of Godhead may become a brahmana, but he cannot become a spiritual master. It is said: sat-karma-nipuno vipro mantra-tantra-visaradaḥ, avaisnava guru asat sat sva-paco vaisnava guruḥ. An impersonalist can become a qualified brahmana, but he cannot become a spiritual master unless and until he is promoted to the stage of a Vaisnava, or a devotee of the Personality of Godhead. Lord Caitanya, the great authority of Vedic wisdom in the modern age, stated:    (More...)
A person may be a brahmana or a sūdra or a sannyasi, but if he happens to be well versed in the science of Krsna, then he is fit to become a spiritual master. [Madhya 8.128] The qualification, then, of a spiritual master is not to be a qualified brahmana, but to be well versed in the science of Krsna.    (More...)

Link to this page: https://prabhupadabooks.com/?qg=6845