I'm probably totally wrong about this, but I'm thinking that when Max says that we can't ever be 100% sure about the authenticity of a guru he means that we can't ever be 100% sure about anything 'external.' Descartes became famous for exploring this. The only thing I can know is that I exist and am experiencing 'beingness' right now. Anything not 'me' could very well be an illusion or a dream. Anything in the past is not evident at all, but only a memory that can be doubted. The only way we can know anything about the 'outside' world is to access it through The Self, by going deep within. This is because the Self encompasses all. That's why the focus on a guru who is supposedly separate and more realized than 'you' is not the most efficient way to realization.
In my own path I found that practices were helpful, even necessary, for a time. Yet since the beginning of the year I've went in a totally different direction, the direction of surrender. Before I felt I had to achieve something or do something to bring about realization. i thought I had to follow certain practices and receive darshan. Now I see that we are on a stream, and the stream is so powerful and good that all we have to do is stop paddling upstream. The stream will take you were you need to go and soon enough you will realize that the stream is you. Just give up any struggle. Decide that you don't have to prove yourself and you don't need or even care about enlightenment. That you don't need anything because you are infinite and completely invulnerable. regardless f what could happen, you will always be. The very fact that it is happening means that it is in divine order, and even if it weren't, you still might as well accept it. Because as long as it is happening you have only 2 choices. Reject it and resist it, which will not change it whatsoever but will only make you miserable, or accept it and go with the flow and the stream that is in Reality your true Self.
Release and relief and even resignation have been 100x more powerful that all the meditation techniques and spiritual books (as important and necessary as they were and are). I used to think I had to actively work on feeling more joy or having more loving thoughts and feelings or opening my heart. Now I see that love, joy, and openness are my true nature, so I don't have to do anything but to stop resisting mySelf. Once I release and surrender after a period of struggle and trying to control, first it feels like immense relief, then it feels like your whole body is just completely relaxed (I was amazed at how this feels because never in my life did I have absolutely no tension in my body or mind...the tension was always there though I was not aware of it because it as 'normal'), and then gradually (and without having to do anything) my heart opens and I am infinite, Christ-like love and joy for all of the universe. So much that I still don't know what to do with it all, I try to send it out but it feels like it will make my body explode! I am both the personal identity of 'Carly' and the impersonal All, and the boundary between the two is fluid and permeable.
It's funny though, even though I know I am the All, I still pray to God and meditate and perform pujas. I telepathically communicate regularly with my sat-guru, Babaji, and also with Jesus, Shiva, and the Divine Mother in all of her forms. I do this because I am also the individualized personality, and this individualized aspect of God is showing reverence to the larger aspect. It is good to keep yourself humbled. To me it is not contradictory. And I know I am not 'there' yet and never will be. I must always be diligent and check my ego and ask to be guided and ask for guidance on allowing myself to be guided and surrendering to my Self. We can always progress and expand. God is always expanding.
I know that release and surrender are the keys to enlightenment and realization. I had had Samadhi experiences, where I was One with Brahman, where the individualized personality disappeared, but now I see that that was only one aspect of God, and was just an expereince and not permanent awakening. I think that when you release more and more until it is a constant state you will be able to shift into Samadhi states at will. It was so simple and easy and right there all along! The idea that we don't have to do anything and the acceptance of the fact that we can't really control anything but that 'this' is perfect is quite possibly the hardest one to accept. I'm still working on it. Well, I'm still NOT working on it!