How kosher is it for a player to suggest ways to challenge a belief? Is that something that is done at BWHQ or a bad idea?
I don’t mind when a player suggests something when I’m GMing. In some ways it lets me know where they are coming from and the types of challenges they think are neat or want to see (particularly true of players I haven’t gamed with much). Although a well-written Belief should be pretty obvious anyway.
With one very important caveat: if I don’t use the suggestion don’t be all hurt about it.
In BW, everyone’s an equal stakeholder in the story, so such advice from players should be welcomed and considered.
Yep agreed Kublai. Just be careful there though, Kublai. What you posted sounds awfully close to “the players can demand how a Belief should be challenged”.
And I would most vigorously disagree with that. 
It is after all the GMs job to challenge Beliefs!
Should consider is totally legit!! And I couldn’t agree more with that.
Sure, I can clarify. Everyone is welcome to suggest ideas, but it’s always the up to the GM to decide.
If the player of a character has a particular idea for how a Belief should be challenged, I think the player should state that outright. Immediately, if the Belief was written with that challenge in mind, or whenever it occurs if the thought comes later. Beliefs are about giving the players directorial input. Players should take it. The GM may disagree, and it’s his/her story too, but it should at the very least be discussed.
As a GM I’m always happy to hear what other players have to say about interesting ways to push Beliefs, or even interesting consequences for failure. At the very least it shows that the players have investment in the story!
We offer suggestions all the time. As Pete said, it’s the GM’s decision on how NPCs act or how situations emerge.
Though it’s also worth stating that we encourage each other to act on Beliefs from a player to player perspective.
And, we’ll challenge each other’s Beliefs—character to character—as a way of engaging.