I'm only up to Daredevil S01E09 so far and Murdock just went to the art gallery to meet with Fisk's Girlfriend. But if I understand this correctly, Fisk genuinely wants to fix the city. So when Murdock was talking to Fisk, why didn't he seem to note that Fisk was telling the truth when he talked about improving the city?
Fisk wasn't lying, so there's no reason to make note of him noticing that Fisk wasn't lying. People that believe what they're doing is right can be dangerous. We have every reason to believe that Matt takes Fisk's plans seriously.
The idea that Fisk believes he is right, as does Matt, are part of the theme throughout the series. Here's an interaction between Matt and Foggy in episode 10:
Matt: We don't live in a world that's fair. We live in this one. And I'm doing everything I can to make it a better place.
Foggy: "A better place." That kind of sounds like what Fisk keeps saying.
Both characters believe they're doing what's right. Foggy here was making that rather explicit for us. Both are violent men. Matt is trying to find out what kind of man he is, and what his limits are. It's also the nature of many of his talks with the Catholic priest.
Is he like Fisk, or is he really a better angel with the devil in him?