It's kinda late, but let me elaborate. I know he want to buy a book, and obviously he needs money(subjugation rewards).
His earning method were to hunt the small fry to get the money. But when the big guy appeared he didn't immediately help and instead asked the subjugation rewards first, why? Don't you think it's weird. It's an emergency, if he didn't kill the boss, he might die... And if he killed the boss he might get some "extra" money (disregarding the amount). And even if there isn't a subjugation reward, he still need to beat the boss for some extras chance of survival. So, I didn't understand why he feel the need to ask the subjugation "reward" instead of thinking of it as a "bonus" money.
TL;DR:
Kill boss = Survive(Better chance) + Extra money(probably).
Ignore the boss = Survive(Less chance) + no extra money.
The answer is simple, kill first then ask reward later, why the need to ask before ensuring safety?