"Sure, that's a good point. I would say I wasn't a demon if I was one trying to trick you. But I'd also say it if I wasn't a demon. I mean, going 'yes I am a demon and I have you now mwahaha!' isn't going to convince you I'm not one."

This argument needs some kind of name. The 'demon paradox' maybe. Or the 'it's impossible to convince someone you're not a demon' problem. Which is a problem because he really doesn't know how to prove he's not a demon. Except by just... not possessing the mage in front of him. But that's sort of a long way to go about it.

The whole uncertainty isn't helped by the niggling sense of familiarity Alistair gets the longer he looks at the other man. He's sure he's seen his face somewhere before, but where?

A Ferelden mage, talking about blood magic and possession. It's not exactly unexpected, given what happened at the Circle. Maybe that's it. A survivor from the tower. ...And that reminds him of something that might help prove he's not a demon. Maybe.

"Look, I got trapped in the Fade by a demon once myself and it gave us all these nice dreams so we'd want to stay. Does this look like the sort of thing a demon would try and keep you trapped with?"