So I'm stuck at this point as well. The quest is asking me to pay 15,000 gold (unless I have a coupon) or fight the troll. First time, my party was around level 8 or 9 and I got the troll to about 25% hp. I left and thought maybe if I did the investigations one of the chests would have the item to reduce the cost, spoiler: they did not.

So now, I figured my party has leveled up a few times, now level 12, it should be a cake walk. Second attempt on the troll was a catastrophic failure. He killed 2 of my party in his first and second turn, both from full health.

Does the game not want you to fight him and instead, grind out the 100 or so fights to get the gold to bribe him?