I don't know why people think say no is a good thing. IMO, he agree with helping her would be more beneficial.
He know nothing about how the world of people with super power work, he need to understand that world right now to fit in. His power will be exposed sooner or later, knowing how the shadow world run is beneficial for him.
She ask for his help and didn't seem like a bad person ( he also have the appraisal skill too, just in case ), he is also strong enough to atleast protect himself right now.
It's time for him to know about the world and she just happen to appear at the right moment, a good relationship with someone from the shadow world is a better choice than just say no because "muh I'm a cool guy who is not swayed by any situation " lol.