It is often argued that leading and teaching are different in the church. It is not the purpose of my entry here. Except that I would just say, I disagree: If one lead a Bible study, one is teaching. So it is not wise to have a rotating "leading" roster that just about any believer in the group can lead.
Now to the main topic:
Should I be asked to lead even when I just joined in, of course most likely I would...not because I accept some recognition, but so that they won't say of me "He just loves to criticize and never do anything himself". However, I would most likely refused first - unless they show desparation, then the usual response would be "He does not care for the group". "On the contrary", I would respond, "I do love the group, and really wish to accept the position and lead, however, let's be clear here, that it is not only I who is being evaluated or approved, but that I am also evaluating and approving you."