Choosing a Spiritual Teacher
The closer to Truth a spiritual teacher, the more clearly they see, the more readily they will be able to facilitate the knowing of Truth in the student. This is the case so long as the teacher can communicate clearly and it is indeed Truth that the student seeks.
Given the student doesn't know Truth (hence seeking it), it is impossible for them to know that any assessment they make of the teacher is accurate. It's common for the student to focus on aspects of the teacher to which they attach meaning/significance. Some examples are: title, age, gender, popularity, claims, certifications, what they wear, how much they charge, how 'professional' their website looks. None of these are reliable indicators of a person's level of consciousness, peacefulness, knowing of Truth etc.
Far easier to identify is the presence of falsehood, disconnection, belief, opinion, stories, heaviness, 'noisiness'... Below are some concrete examples.
Ego-bolstering: you're amazing, wonderful, perfect, special, your vulnerability is a strength, your sensitivity is a gift, your scars are beautiful, you deserve the world, you have the right to feel/have/experience, own it!
Closed-heartedness: you are nobody, you are nothing, I will give you the cold, harsh truth about reality
Vague language without exploration, explanation or clarification: the universe has your back, everything happens for a reason, everyone is different, just be present
Cause and effect: you are experiencing this because of that, x causes y, this is why that is happening
Blame/powerlessness: they impacted you, they made you feel, of course you reacted that way, it's not your fault, they need to take responsibility, you are the way you are
Judgement: good, bad, right, wrong, should, shouldn't
Instruction without context or mention of consequence: meditate for one hour a day, don't drink alcohol, never pee with the door open
Belief: I believe that we are, we aren't, there is, there isn't, I believe in miracles, God, jumanji
Pride: look at me, look at what I know, be proud of yourself, be humble
Weight: this is important, significant, meaningful, this matters, respect and honour life, nature, this teaching
It is not the case that teachers (or anyone else) who display any of the above won't help you in your search for Truth. However, if you do progress spiritually and continue to do so, incongruencies will eventually be noticed, and at that point, if you don't pay attention to such incongruencies, it's likely you'll become 'stuck' at the level of the teacher. This is especially likely if you 'look up to' the teacher (i.e. if you experience separating concepts such as trust, honour, respect etc), as it's likely you will to pay more attention to what the teacher says than to the clash/conflict that is your own experience/knowing/sensing of falsehood.
I've worked with around ten spiritual teachers and benefited from each. The only person I've met 'in real life' with whom there is no clash/conflict is my boyfriend, Alex.
Some Sources of Truth/Upliftment
Eckhart Tolle - The Power of Now, A New Earth
Neale Donald Walsch - Conversations with God, Books 1, 2 and 3
David R. Hawkins - Letting Go, The Eye of the I, his Map of Consciousness