The dialogue part with tadeas is not intentional and most likely a bug. I will look into it. Tadeas talks about the ambush with you the first time you talk to him, but he says it was him who got ambushed. It basicaly tells you to expect trouble.
Refusing the quest is just a roleplaying option and doesn’t do much else
Taking the money and finishing the quest is also intentional. When I was making the quest, it seemed to me like something someone would do. Take the money and then continue doing the oposite anyway.