While Jesse often speaks from his heart, he is a fairly reliable narrator because he is objective in attitude. For instance, in Chapter 1, Jesse remarks of his friend Rise, "Even when I wasn't sure he was right, I listened to him carefully." Further, he seems wise in his depiction of Mason,
The way he sees things, there's him and there's the rest of the world. he's being righteous and the rest of the world spends all day trying to mess with him....Mason didn't do anything I could tell but hang around the block. But like one of the old West Indian dudes said after he and Mason got into an argument--he just felt like trouble.
Regarding Sidney, the policeman, Jesse is also objective, narrating that Sidney is "righteous"; he deserves respect. And, yet, Jesse is able to be humorous, too. In Chapter 3, he observes that one of the things that he likes about his father is that "it was only him and me who did stupid things around the house."
In addition, there is much dialogue recorded by Jessie, the use of which lends trustworthiness to his narration as the exact words of the people are an objective recording in which no judgments are made.