1) Who can deliver the Conditioned Soul and who is Eligible to occupy the post of guru?

Srila Prabhupada…"No demigod can perform this act of delivering the conditioned souls, because the demigods themselves are conditioned. A conditioned soul cannot deliver another conditioned soul. Only Krishna or His bona fide representative can deliver him." 
—–NOD – 1970 Edition: Further Consideration of Devotional Principles

 2) Srila Prabhupada…"When one has attained the topmost position of maha-bhagavata, he is to be accepted as a guru and worshiped exactly like Hari, the Personality of Godhead. Only such a person is eligible to occupy the post of a guru.” 
—–Sri Chaitanya-charitamrita – 1975 Edition : CC Madhya 24:330

3) So our business is to accept a bona fide spiritual master, being guided by him, to follow the rules and regulations. Then advancement is sure. There is no doubt about it. And if we become hodgepodge and mix with hodgepodge and do hodgepodge, there is no progress. 
——Srila Prabhupada Srimad-Bhagavatam 6.2.24-25 — Gorakhpur, February 13, 1971

4) Devotee: If someone is actually sincere, can he be cheated, or will he always get a bona fide guru?

Prabhupada: No, if he is sincere, he'll get….Yes. Because you want to be cheated, you go to the cheater. That's all.
——Srila Prabhupada Morning Walk, Los Angeles, December 7, 1973