There is only one way to know definitively if someone is a master of the white lodge: awaken your consciousness in the superior worlds and investigate them there. Anything less than that is unreliable. That is why Samael Aun Weor gave this strict instruction:

"This is why we advise our disciples not to follow anyone. Let our disciples follow their own Self. Each of our disciples has to follow their resplendent and luminous inner Being. Each one has to adore their own “I Am.” We beg, beseech, our disciples not to follow us. We do not want henchmen or followers. We have written this book so that you, our friends, listen to your own internal master, your resplendent “I AM.” The Innermost is your master: follow Him. First, take heed that none of the many false avatars who appear during these times deceive you, for many impostors appear in these times and deceive others. Second, take heed of sexual temptations. Third, do not ever attend spiritual centers; the mediums-channelers can easily lead you astray from the path. Many disciples have fallen horribly due to these three dangerous reasons. Flee from these three treacherous dangers so that you may not lose your initiations and degrees." —Samael Aun Weor, The Major Mysteries

“I do not follow anyone; therefore no one should follow me.” —Samael Aun Weor, Practical Astrology

There are always many people humbly proclaiming themselves to be masters. Sadly, modern people mistakenly believe they need to follow a "master" in the physical world. This is a grave error, propagated by those who benefit from the mistake.

You do not need those "masters" to walk the path. In fact, quite the opposite is true: by submitting to yourself to some external authority, you no longer seek to hear the voice of the real master, who is within you. 

"There is a need to search for a guru in order for him to guide us along this internal and delicate way. The guru must be searched for within, in the profundity of the consciousness... Each disciple must search for the master inside, inside, inside. The master is found in the profundity of our consciousness. If you want to search for the master, abandon all bookish erudition and pseudo-spiritual schools. The master appears when the disciple is prepared." —Samael Aun Weor, Igneous Rose

"...in this day and age, it is very dangerous to just simply follow someone. What is best is to seek the Inner Master. The best thing is to follow our “I Am.” The best thing is to learn how to travel in the Astral Body in order to visit the temples of the White Lodge and to receive the teachings directly in the temple...

"Authentic degrees and authentic white initiations are received in the consciousness. These initiatic ceremonies are performed within the superior worlds. Initiations are intimate realizations of the consciousness, which must not be revealed, or spoken about. No one can grant initiations to anyone. Initiation is attained through life itself. In this day and age, everybody wants to be a master. Notwithstanding, we state that there is only one master; this is the inner Christ that enlightens every human being who comes into the world. Thus, only Christ is the Master. Only the resplendent “I Am” is the Master."  —Samael Aun Weor, The Major Mysteries

Here is what Jesus said about "masters":

"The scribes and the Pharisees sit in Moses' seat: All therefore whatsoever they bid you observe, that observe and do; but do not ye after their works: for they say, and do not. For they bind heavy burdens and grievous to be borne, and lay them on men's shoulders; but they themselves will not move them with one of their fingers. But all their works they do for to be seen of men: they make broad their phylacteries, and enlarge the borders of their garments, And love the uppermost rooms at feasts, and the chief seats in the synagogues, And greetings in the markets, and to be called of men, "master, master." But be not ye called master: for one is your Master, even Christ; and all ye are brethren. And call no man your father upon the earth: for one is your Father, which is in heaven. Neither be ye called masters: for one is your Master, even Christ." —Matthew 23

Signs of a False Master

The easiest way to separate pure from impure is on the basis of chastity: a genuine master knows that the path of liberation requires sexual transmutation. However, that is not foolproof: there are many black magicians who preserve their sexual energy. Yet, they do not eliminate the ego. Read Treason by Samael Aun Weor to learn more.

"The disciple who wants to enter the straight, narrow, and difficult path that leads us to the Light has to withdraw from all spiritual schools. Those schools are filled with “sublime crimes.” Those schools are golden cages filled with “very beautiful poisonous vipers.” Mystical evilness is very abundant in those schools. The worst crimes registered in the penal code are committed under the shelter of the divine phrase “Universal Fraternity.”... We have known horrible cases. I.e. we knew the case of a certain hypocritical pharisee who passed himself off as Jesus Christ... later he alleged that he was uniting all the schools, orders, sects, creeds, and lodges within a universal fraternity—and he was the center of it all, naturally. We knew about another subject who took the name of K. H. in order to declare that he was an Avatar, and that he should reunite all the schools under his scepter. All these types of opportunist subjects usually found black lodges under the shelter of the beautiful phrase “Universal Fraternity.”... Therefore, we advise our disciples to be very careful, it is better to withdraw from these types of ladies and gentlemen, because they are dangerous and deceitful." —Samael Aun Weor, The Major Mysteries

Signs of a Real Master

"The authentic master never boasts of being a master... An authentic guru does not go around boasting about it. The authentic guru is the Inner Christ. A true master goes around everywhere anonymously and unknown. He does not exhibit his deeds or powers, and is filled with modesty. A true master is before anything else an upright citizen. The authentic master is never an intellectual, since the intellect is an animal function of the human “I.” The true master is like a child, pure, holy, simple, and natural. The true master is the Inner Christ “that is the true Light, which lightens every man that comes into the world” [John 1:9]." —Samael Aun Weor, The Major Mysteries

"...the authentic female enlightened masters never go around boasting about it. The true disciples and masters are those who know how to consciously travel in their astral body. The male and female devotees who remember their past lives and who can astrally attend the temples of mystery are true enlightened beings, yet they never go around boasting about it; these are the ones who really know." —Samael Aun Weor, The Major Mysteries

Learn more: Seeking the Master: Teachers and Students