I think you are proceeding backwards in your example.
First the players should understand why the guards are not letting people in.
Then maybe find out who/what kind of people would be welcomed in.
Then formulate a plan accordingly and execute it.
Fictional basis is key IMO, as you mentioned upthread.
Conan the barbarian (1982): Conan wants to bluff the guards, disguises himself as a white robed cultist among a multitude, guards let him in.
Simple as that.
Also,
@Ovinomancer , is this sidestepping the rules, or skilled play?
In B/X there are no skills, nor Charisma is not exactly supposed to be used for bluffing