We validate the truth of Buddha's teaching by experiencing the truth ourselves. After putting one teaching into practice, we will experience beneficial changes in our lives, this will inspire us to learn more about all the other teachings of the stages of the path.
Similiarly, in order of understand how each Buddha, Bodhisattva or Dharmapala uniquely contributes to our understanding & experience of the Dharma, one only needs to spend some time doing some research on the nature & function of enlightened being concerned, learn teachings related to His/Her nature & put them into practice. Throughout the process of putting the related teachings into practice, rely on the enlightened one for inspirations on the basis that you are on the same page with Him/Her now & observe your experiences.
It is just like to trying to understand someone around us. We will spend some time talking to them to understand their opinions on various issues of life. We will hang out with them to learn their habits. We tell them secrets & give them responsibilities to see if they are trustworthy. After a while we will have an idea of how the person is really like.
We do not rely on hearsay to judge a person around us, not to mention an enlightened being.
I can describe to you how a particular dish taste like, but until you try it yourself you will never truly know.
Among all Dharma Protectors whom I rely upon in my life, I experience for myself through doing the above that Dorje Shugden is the most responsive to me, hence I mainly seek refugue in Him.