I actually had the very same feelings as the OP doing that quest here. Not that I want to play the lawful good guy but there are some things I don't like doing. The way this particular quest laid out for me was like that:
- I was helping a guy who wanted to clear out a haunted house.
- When inside the house, the Deadric lords goes nuts and closes all doors. Only way to get out is to kill the other guy that entered with you. At least - if you wait a bit - he attacks you first so no issue there.
- The door to the outside doesn't open still. So you have to get your reward in the cellar and be trapped by the Deadric lord.
- He tells you about a priest that is wounded and captured somewhere in the wilderness. He wants that guy to return and do a ritual so he can get his soul. I tell the lord "gfo, not doing it". so I am released.
So far so good. But here comes my first mistake: I thought since I now know where the wounded priest is held captive, I will free him and warn him never to return to that hautned hause cause there is a trap laid out for him.
So I rescure the priest but the only dialogue options I have are only to threaten the priest in the name of the Deadric lord or do not reveal any info. So the priests heads off to the house to fight the Deadra lord.
Here comes my second mistake: I still think I can save that whole mess by following the guy to the house and help him or at least warn him there of the trap.
All wrong. The priest gets trapped by the Deadric lord and the only options left for me are
a ) leave the priest there so he can starve to death
b ) kill him off fast ... but that doesn't work either cause if you kill him too fast, the Deadric lord just resurrects him and you have to try again.
So I end up wounding the priest so he begs for his life and the Daedric lord gets his soul.
So, long story short. I understand the sour taste that leaves in the mouth of the OP. The only real solution would be to walk away from the house and don't try to save the priest and don't care about the Deadric lords offer. Problem in my case was, I thought there might be a different option until it was too late to get out of there in a decent way.
So far this is the only quest I did that left me with that strange feeling.