[X] Begin by just asking him more about his life and his reasons for coming to the Hading and what he expects out of working with us, using our various lie detection stuff and Odr-boosted Goal Tell to see what he's being truthful about in his answers. Depending on how he reacts to these questions and what his answers are, either turn him down with a carefully worded non-lie about spiritual advice (specifically, get Blackhand's advice on what to do with Skavidr and say that a family spirit does not advise hiring him), or tell him we, by luck, caught him spying on us and demand answers.
[X] Just tell him the (partial) truth right away. We saw him reporting to someone when we went out, and we cannot trust him. Set the tone immediately and see what excuses he can come up with, while fueling our lie detection and goal reading stuff to see where he lies and when. Proceed to call him out on every lie we detect, and metaphorically rake him over the coals.