Berachos 28a - Tefillas Arvis R'shus Oy Chovah - Part III

Gemara: "It was stated: That day [that Rabban Gamliel was removed from the office of Nasi] they removed the doorman, and the students were given permission to enter. For, Rabban Gamliel would announce, 'Anyone who is not as sincere internally as he appears externally may not enter the Bais HaMedrash.'"
The question is, how would the doorman know who was completely sincere and who was not?
Two possible answers:
1) Perhaps the doorman didn't let anyone in. If a student managed to somehow get in anyway to be able to listen to the shiur, this proved his sincerity.
2) Perhaps the doorman was there to charge an admission fee - if someone paid, that showed his sincerity - that he was willing to part with money to enter the Bais Hamedrash.
I prefer the second answer, because we find elsewhere is Shas that in the time of Rabbi Akiva there was an admission fee. (Sorry - I don't remember where that gemara
is.)