if someone gets some kind of information that could spoil the party for those who don't want to know anything before the shows, post that info under the advertisement
SPOILER - [topic title] - SPOILER.
And the title cannot have such information, obviously. If it's a rehearsal, dont say "SPOILER - They are rehearsing Acrobat!!" or something like that, it's the same spoiling after all. Just make a little effort to make sure that people who doesn't want to know, really don't know. That's how it has to be done, such people won't enter the topic and that's all. It's easy, and that way we can keep everyone happy.
Thanks.
The Crew
