They'll just refuse to give him more shards and give him the cold shoulder if he presses them about it.

The crows don't talk, so he has better luck doing it on his own. After he does the Cornerwitch magical question ritual, the graffiti reveals that the crows think Anna Monday is too dangerous to leave be. Clearly they know something everyone else doesn't. (Its violence and instability will be more properly showcased as the next rescue party obstacle.)