Heh. Should have known this would come up. My poor, poor main characters.
Long story short: “Um, in a world where illusions work – what happens when the defense lawyers find that out, and every case with eyewitness testimony is now up in the air?”
There are, in various kinds of folklore, ways to see what’s real. But most of them take preparation in advance, and all of them have the problem that if you see Something, It may realize you’re seeing It, and not take that kindly.
Myrrh’s also going to have to admit part of what she tells them is informed guesswork – due to her past, Seeing is effectively default mode for her.
Oh man am I glad I’m not a lawyer in this world!