So all it takes, for an experienced player to avoid being called a dirty metagamer (and having his declared actions shut down), is to take the time to write a 300 page background that can virtually guarantee they will cover most nearly any traditional "gotcha" information that may arise at some point during play?*And here it would probably depend on each character's background.
I get you are saying "might very well" for both. But these are still thin, arbitrary reasonings. IMO, they just as easily "might very well" be the opposite. The militiaman could be a fresh recruit who hasn't had that particular bit of information drilled into him yet (there's just so many scary things that go bump in the night - it takes time to get a green soldier fully up to speed). Meanwhile, the farmer's late, great-grandmother could have been bitten by a werewolf while gathering firewood in the forest way back in the day. Sure, she was eventually cured by a wandering witch who took pity on her after she accidentally killed her husband during one of her "episodes". But her descendants still fear some hint of the savage wolf spirit still resides deep in their souls, just waiting to resurface.A local militiaman might very well know what those silvered arrows are for, having had it drilled into him by his commander. A farmhand might very well not, having never heard of lycanthropes in his life.
[*Someone earlier in this thread made mention of how much s/he like using hyperbole to illustrate the ridiculousness of a position. - Thanks for the advice, dude!**]
[**I don't remember who it was and I'm far too lazy to go back and fish it up.]