I think recruitment should be handled as an inRP process. If a character isn't accepted for whatever reason, I'd treat it as a role-play occurrence. If the character cares about the cause involved, they'll have to find other ways to support it. Alternately, if I really wanted to be a part of a faction, I’d write a character that would fit in with the requirements for it. Ultimately, joining a faction should be an outgrowth of a character’s RP, and one should flow naturally from the other. If it doesn’t, then the character’s likely not suitable for the faction.
