You can technically get Blood Magic in a non-bastardy way if you have Master Coercion and okay Strength, enough to make the highest intimidation check in the game. It's what I did, since getting it normally would otherwise have frightened me off.
Irving: "Now remember, desire demons like to tempt people with offers. Don't bargain with demons, it never works out."
Me: "I understand, master. I won't bargain with it."
*steps into the Fade*
Me: "Welp, he didn't say anything about not extorting demons!"
*finds demon*
Demon: "You're pretty strong, so I doubt I could take you in a fight. Tell you what, how about I leave for a while, and only come back later?"
Me: "I have a better idea. I'm here, you can't beat me, so you're going to leave the kid. Permanently, end of discussion. Now, what will you give me so I don't rip you apart?"