Jules doesn't argue anything Crowley says, he he doesn't believe of word of it either. If Crowley is paying enough attention he can probably hear Jules muttering to himself as he walks away.

"Minsid hell, "I owe you one?" This place must be more screwed up than I thought if it can alter reality that much."

Nobody ever owes him one. He's the one who will be constantly paying back debts to karma.