Srila Bhaktisiddhanta Maharaj writes in the book Brahmana and Vaishnava....
..."If an initiated person has not undergone the sacred thread ceremony, then according to the statement of Brihaspati, a compiler of Dharma shastra, he has simply transgressed religious principles. The scriptures state that after receiving initiation one becomes twice born. If this was not so, then it is to be concluded that he has certainly not been properly initiated. If one is properly initiated then the results must come. A cause is known by its effects. If one claims to be a Vaishnava guru while neglecting the tat tenaiva vinirdiset verse, ("he should be accepted according to those symptoms of classification" statement of Srimad Bhagavatam 7.11.35), then he should be rejected. This is the purport of the scriptures.
One who assumes the dress and position of an acharya, who speaks against conclusions of Srimad Bhagavatam and other scriptures or who performs kirtan opposed to the proper glorification of Sri Krishna, certainly goes to hell for countless lifetimes along with his disciples and whoever else hears such non devotional talks and kirtans...."
The above reference to Srimad Bhagavatam is 7.11.35 -- If one shows the symptoms of being a brahmana, kshatriya, vaishya or shudra, as described above, even if he has appeared in a different class, he should be accepted according to those symptoms of classification.
And in Srila Prabhupada’s purport to Srimad Bhagavatam 8.20.1 -
Anyone who is supposed to be a guru but who goes against the principle of visnu-bhakti cannot be accepted as guru. If one has falsely accepted such a guru, one should reject him. Such a guru is described as follows (Mahabharata, Udyoga 179.25):
guror apy avaliptasya
Srila Jiva Gosvami has advised that such a useless guru, a family priest acting as guru, should be given up, and that the proper, bona-fide guru should be accepted.
The pseudo religionists have neither knowledge nor detachment from material affairs, for most of them want to live in the golden shackles of material bondage under the shadow of philanthropic activities disguised as religious principles. By a false display of religious sentiments, they present a show of devotional service while indulging in all sorts of immoral activities. In this way they pass as spiritual masters and devotees of God. Such violators of religious principles have no respect for the authoritative acharyas, the holy teachers in the strict disciplic succession. They ignore the Vedic injunction acaryopasana --"One must worship the acharya" — and Krishna’s statement in the Bhagavad-gita (4.2) evam parampara-praptam, "This supreme science of God is received through the disciplic succession." Instead, to mislead the people in general they themselves become so-called acharyas, but they do not even follow the principles of the acharyas.
These rogues are the most dangerous elements in human society. Because there is no religious government, they escape punishment by the law of the state. They cannot, however, escape the law of the Supreme, who has clearly declared in the Bhagavad-gita that envious demons in the garb of religious propagandists shall be thrown into the darkest regions of hell (Bg. 16.19-20). Sri Ishopanishad confirms that these pseudo religionists are heading toward the most obnoxious place in the universe after the completion of their spiritual master business, which they conduct simply for sense gratification.
Srimad Bhagavatam 1.19.37 Purport - The Appearance of Sukadeva Gosvami
Unless one is perfectly anxious to inquire about the way of perfection, there is no necessity of approaching a spiritual master. A spiritual master is not a kind of decoration for a householder.
Generally a fashionable materialist engages a so-called spiritual master without any profit. The pseudo spiritual master flatters the so-called disciple, and thereby both the master and his ward go to hell without a doubt. Maharaja Parikshit is the right type of disciple because he puts forward questions vital to the interest of all men, particularly for the dying men. The question put forward by Maharaja Parikshit is the basic principle of the complete thesis of Srimad-Bhagavatam.
CONCLUSIONS - So many come in Kali yuga and claim they are Guru - but the Srimad Bhagavatam says one should judge these persons by their behavior first, then such persons can be classified as Brahmana, Kshatriya or whatever. If one sees that a person who is claiming to be Vaishnava guru doesn't even chant 16 rounds, the minimum given by his own guru, then what kind of guru is he? If this same or similar person has also been found to be engaged in sinful acts, then how is he guru?