"As for the miracle where a certain person by means of a sign or vision... by hearing the voice of human beings, non-human beings, or devas... by hearing the sound of the directed thought & evaluation of a person thinking directed thoughts and evaluating, [saying,] 'Such is your thinking, here is where your thinking is, thus is your mind.' ... [or] who by having attained a concentration devoid of directed thought & evaluation, and encompassing the awareness [of the other] with his own awareness, he discerns, 'Given the way the mental fabrications of this venerable person are inclined, the directed thoughts of his mind will immediately think about this.' And however much he may read, that's exactly how it is, and not otherwise: that is a miracle experienced only by him who does it; it belongs only to him who does it. It seems to me to be of the nature of an illusion.
"As for the miracle where a certain person gives instruction in this way: 'Direct your thought in this way, don't direct it in that. Attend to things in this way, don't attend to them in that. Let go of this, enter and remain in that': this is the miracle that, of the three, appeals to me as the highest & most sublime.
AN 3.60 Sangarava Sutta: To Sangarava - translated from the Pali by Thanissaro Bhikkhu
Simple observation of people can inform us of how people are thinking, as we all follow a set of routines which can then be predicted when observed closely enough, this is no secret, it is how psychological illusionists perform their tricks, and how psychology works. This form of mind reading can be useful though, as we can internalise the external observation of others and use it to see how we operate, a reading of our own mind, which is far more useful than reading others minds.
To see how we function and what works for us on a day to day basis in practice increases our ability to help others, as we see what doesn't work for us, and communicating with other practitioners can inform us further as to what works for them, or how things work for them, this communication leads, when put to the test for ourselves, to an even greater ability to instruct others. However the ability to instruct others should be teamed with personal daily practice, practising what you preach, and preaching what one practices.
The Dhamma, or truth excels all gifts, and is not a commodity for sale! This is part of what keeps Dhamma (in its sense of teaching) pure, as Ajahn Chah once pointed out, if you practice well, support will be there, if you do not, then there will be less or no support, and this is a guiding principle for all to keep in mind, the dhamma is our refuge; “Those who practice the Dhamma are protected by the Dhamma.” and if we are not treating the dhamma as a commodity then we have the Dhamma as a refuge, and the teaching of truth is more likely to be coming from a skilful place from us.