I see your point, Sami, but it is the sage who comments on the PC's herb lore. With your approach I would have the sage ask if the PC's herb lore is good ("You don't happen to know your way around the local plants?"), as well as allowing the PC to back out gracefully when the plant sought is revealed if it's unknown ("Sorry, that's a plant I don't recognize"). After all, a herb lore skill of e.g. 50 isn't bad, but it's still far from sufficient to recognize everything the sage may request, and the sage might have more need of legwork than skill in some cases, so an acceptance in the first phase might not reflect over confidence.