Truth

In writing my reading response I have run into a question that maybe others can help me with. Plato mentions (according to Herrick anyway) that true (good) rhetoricians must be philosophers like himself. They must not be seeking to persuade others to their own points of view, but rather guiding others to Truth.

Does Plato/Herrick mention anywhere how Truth is to be verified? Other than that it is arrived at via much study and contemplation. Who gets to decide what Truth is? 

Hitler and St. Augustine respectively did massive amounts of research in the quest for Truth. Who's version would Plato find legitimate? Who gets to be the leader of the masses, whose love of honor and appetite outweigh their love of wisdom, and therefore should voluntarily submit to the lovers of wisdom?

I think there is no answer, but perhaps I missed something in the massive amounts of reading (wink) that indicated how Plato felt about this.