Right now William is just trying to get a sense of the situation. Aside from the three he is with, the other people with powers he has come across have been less than good company.
I had a 90% chance of rolling higher than 11, and I get 11. If I wasn't trying to gather evidence I wouldn't have bothered with the reroll. I am thinking of playing off the sense motive check as a general distrust more than knowing Rasa lied about it's/his/her name for story sake.
So does the feeling our characters get when around others with powers tell us if they are good or bad? For example, if we ran into a mass murdering powered person would it feel different compared to a powered person who heals the sick?