I checked this today, the dialogue that originates the quest contains a strong warning but the journal entry is an urgent call to action - mixed messages.
I think it would be reasonable for the mercenaries for the mercenaries to give several warnings unless the party is high level and that the warnings which should be very matter of fact (no bragging or boasting):
*Go away, we are busy and don't have time to deal with unimportant matters*
A few corpses about the place might help too.
It might be simpler though for the quest not be given until the party reaches a suitable level or acquires a strong reputation in Stalwart.