Eh, I know nothing about how to handle most dangerous animals, even ones that live in my area; I’d imagine that even in a world with trolls, regular people wouldn’t know anything about them.
If your character is a seasoned adventurer or monster enthusiast, sure, light it up, but if your backstory places you as the village baker for most of your life, running in with alchemist’s fire at the ready seems a bit strange.
Ultimately I’d consider it to be on the GM’s shoulders - if the only way your group is going to survive the troll encounter is with fire, then put an NPC in the local tavern who warms newcomers of a troll in the area, recommending that they have a lit torch at the ready.
Funny that you use those examples, since they’re both wrong. If anything, we should be running at the trolls with stinky socks because someone wanted to sound smart at a bar once and made up a factoid that spread like wildfire among the common folk.