Should You Stop the Second Charleston? Four Teachers Disagree
The rule is settled and the tactic is not. Here is who says what, so you can pick a side knowing it is a side.
Most mahjong questions have an answer. This one has four, all from people who teach the game seriously, and pretending otherwise would be doing you a disservice.
First, the part that is not in dispute
The second Charleston is optional. Any one player may stop it, without giving a reason and without anyone else's agreement. The window is narrow and precise: say it after the first left, and before anybody has picked up the tiles from the second left. Once someone has, the whole second Charleston becomes mandatory.
Plenty of sources write this as "everyone must agree". It comes to the same outcome, but it reads as though you have to collect consent, and you do not. One person saying no is enough. You will also see it called a vote. It is not a vote.
Stopping does not cancel the courtesy pass. That happens either way — and equally, running the full second Charleston does not cancel it either.
Now the part that is
Four positions, all attributable, none of them obviously wrong.
Stop it almost always
The strongest version comes from teachers who argue that by the end of the first Charleston you should already be pointed at one or two hands, and that further passing mostly helps the people who are not. Missy Mahjong takes roughly this line.
Continue while you still have three tiles worth losing
The most common position, and I Love Mahj states it plainly: the passes cost you nothing as long as you genuinely have three tiles you do not want. The moment you are passing tiles you might need, stop.
Elaine Sandberg's book gives the practical corollary — if you had to blind pass on the first left, that is your signal, because it means you already could not find three.
Stopping is a weapon
Tom Sloper treats the decision as tactical rather than housekeeping: stopping denies the other three a round of improvement at a moment when you may be further along than they are. He also says openly that he is in the minority on this.
Stopping invites retaliation
Experienced players on public forums point out the social cost. Stopping tells the table you liked your hand, and the courtesy pass is immediately afterwards — where the player opposite you now has a reason to offer you nothing. I Love Mahj independently describes that retaliation as a real tactic rather than a hypothetical.
What to actually do
I am not going to resolve it, because it is not resolved. What I will say is that the four positions disagree less than they appear to: three of them are really asking the same question, which is whether you still hold three tiles you are happy to lose.
The genuine split is Sloper's — whether to stop when you do still have junk, purely to deny the others. That one is a judgement about the table you are sitting at, and it is the part no article can decide for you.
Whatever you decide, say it quickly. Once someone has picked up their second left, the decision is made for you, and hesitating is how that happens.
Where this comes from
The rule — any one player may stop it, before anyone views the second left, with the courtesy pass unaffected — is confirmed by the American Mah-Jongg Association's rulebook, Tom Sloper's rules FAQ and Elaine Sandberg's Play American Mah Jongg!.
The four tactical positions are attributed above and are opinions, not rules. American mahjong has no authoritative strategy: what circulates as consensus is the overlap between a handful of teachers, and this is a question where that overlap runs out.