Sesto thought about Andruss the Dusk and his claim about Maccath the Crimson. It was clear that Andruss was taking advantage of the situation, but it seemed unlikely that he would lie about her absence. In fact, if Imani's Agents were to perform the task for Andruss and he did not produce information on her whereabouts, it would be an obvious violation of basic deal-making. While the Arcane Brotherhood had a mixed reputation at best, they were not known to back out of a deal, in particular one that benefited them at very little cost.
No, it seemed to Sesto that it was likely true that Maccath the Crimson was not present. The bigger question was: What would they have to do for Andruss to tell them where she was, and when he did, what would they have to do to get to her?