Buddy we’re playing adventurers who are by their nature main characters. We can’t Dues-ex everything but we can know things. Also who’s to say we’re city dwellers? Both my last characters lived well outside city limits. And when you live in a world with actual trolls you don’t think their children’s stories would have key information like that? How many of our own children’s stories include warnings? How many myths and legends? Hell the bible likely said to not eat pig because it made people sick and everyone thought it was some will of god shit so they stayed away.

If I made a player roll for it, say their character really probably wouldn’t know, then I’d make that shit a DC 5. Like, “everyone else knows it but you missed that lesson, sorry.”

Making characters stupid for “realism” based in a misunderstanding of how either world works is just boring for nothing.