Rupa Goswami cites verse SB 11.3.21 in the Bhakti rasamrta sindhu to describe both the guru and the disciple. Gopala Bhatta Goswami also cites this same verse in his book Hari Bhakti Vilāsa in a similar context, and Sanatana Goswami elaborates on it further in his commentary. Maharajji’s translation of the book and commentary from the Sanskrit into Hindi is here.

The verse is as follows –

tasmād guruṁ prapadyeta jijñāsuḥ śreya uttamam
śābde pare ca niṣṇātaṁ brahmaṇy upaśamāśrayam

Therefore, one desirous of knowing the ultimate welfare should resort to a teacher who is well versed in scripture, has realized the absolute reality, and thus is fully peaceful.

The qualifications of the teacher then are as follows. He/she is

• śābde niṣṇātaṁ – expert in the knowledge of sastra.
  • The word niṣṇātaṁ means that a person is drenched in knowledge, like one is drenched when taking a shower.
• pare niṣṇātaṁ- has realization of it.
  • The guru is also drenched  (niṣṇātaṁ) in experience of parabrahman, and not only knowledge.
• Practices it in his/her own life.

To recognize a genuine teacher is not easy. The śābde niṣṇātaṁ part may be easier to determine. One can inquire about

1. Whether the guru spent a significant amount of time with their guru (several years). This is recommended by Gopala Bhatta Goswami in the Hari Bhakti Vilāsa (pp. 32 onwards at the link above).
2. Whether the guru took systematic training in the different darśanas.
3. Whether the guru is well-versed in Sanskrit, the language of the scriptures.

These are some basic standards that should be met. Of course, it is not possible to discern the pare niṣṇātaṁ part for any disciple.   

The qualifications of the disciple are as follows. He/she

• Takes shelter of the guru. (guruṁ prapadyeta)
• Is inquisitive about that which brings the supreme benefit, which is uttama bhakti. (jijñāsuḥ śreya uttamam)
  • This means that the disciple must be detached from material enjoyment, otherwise he/she will not be interested in uttama bhakti.