Personal development is a huge business. Gurus abound. Most people want to get better at something or reduce stress in their life and need a teacher. Parts of truth can be shared in many ways and by many people. Sometimes a person just needs to hear how great and unique they really are as an individual. This can be a stepping stone to understanding one's potential. The gurus are seeking to unlock performance and free people from the inhibitions that limit them.
Life coaches have proliferated in recent decades in part because corporations and individuals must compete in society. All these teachers can do is sell you on the idea of becoming better. They do this either by using themselves or others as an example. Some know how to teach certain aspects of it very well.
How well do they apply their own teachings? Success is really so subjective. A teacher/coach/guru may have unsettled personal relationships yet achieve financial success and social status. Are they happy. We never really know until they make some confession or they get exposed. How many preachers have been exposed for various scandals. Some mix their brand of preaching with personal development.
I have been a student of success, achievement and personal/character development since I was about 18. Possibly before that but conscientiously probably not. I am a student because I have never crossed the threshold of being what I would consider a teacher, even though I teach about the principles when I get an opportunity. I only consider it student teaching to reiterate to myself and to see if I am internalizing what I learn. Because I am not a teacher I also might express some things that others would stay away from.
Personal development is about knowing and following truth and as such it must have a spiritual foundation.
Can leadership gurus, preachers, life coaches or spiritual advisors give you real spiritual power? Even when they invoke any aspect of the divine association they still make no claim on power beyond the grave. With good reason. They generally know better. Most understand the position of integrity they must maintain and the limits they can go without risking credibility to their audience. They also know that they want to appeal to a broader audience and therefore don't usually use their faith as a format.