Sacred Haven of Debauchery

Rude remarks. Even the manual explains what each symbol means.

So, I was right when I said that killing the cursed renegade on the spot would be a good choice for you?

Orsino knew that Quentin was insane, but he was afraid to tell anyone (Orsino himself says this, and he knew that Quentin was killing people). Quentin lured women using blood magic; this is clear if you read the dialogues.

It seems we read different dialogues. However, I'll leave that to your conscience.

Blood magic comes from communicating with demons, and there is a high risk of becoming possessed.

But that's not the case. A perfect example is Jowan – an inept mage; they didn't want to send him to the Trials – obviously, out of fear that he would become possessed. Nevertheless, he successfully uses blood magic without any possession, and without demons, by the way.