Many years ago a young yeshiva bochur suddenly apeared at Yeshivat Hakotel on Rosh Hashana night. He asked the Rosh Yeshiva [Rav Hadari] if he could eat there. The Rosh Yeshiva asked him where he was from. The boy explained that he was learning in Yeshivas Netzach Yisrael in Rechavia under HaRav Gustman [ztz"l] and he had been set up by the yeshiva to eat a meal at the home of a certain family. He didn't trust the kashrus of this family and told the yeshiva this. The Rosh Yeshiva promptly expelled him from the yeshiva. If you don't trust us to set you up with a family that keeps kosher, explained the Rosh Yeshiva, then you have nothing to find in this yeshiva [in Hebrew they say אין לך מה לחפש פה].
This Motzaei Shabbos I was at the tisch of the Tolna Rebbe Shlita. I was sitting near a boy who had never been there before and learns in one of the top yeshivos in the world. He whispered to me "What is the hechsher of the food here?". I answered that I don't know.
What maybe I should have answered was "If you don't trust the kashrus of the Rebbe Shlita, then what are you doing here?? We are all here to learn from and absorb the kedusha of the tzadik. If in your mind he might not even be religious enough - then you should be spending your time doing more constructive things, like sitting in the beis medrash."
In order to be mekabel from someone - it is critical to have respect for the person, both religiously and otherwise. Having a Rebbe or Rov is critical - but the sine qua non is to be a proper כלי קיבול [receptacle].