Miss Maudie doesn't believe the rumors about Boo Radley at all.
In Chapter Five, Scout enters into a discussion about Boo Radley with Miss Maudie. In the middle of the conversation, Scout pointedly asks if Miss Maudie believes everything people say about Boo.
Miss Maudie believes all the stories about Boo were made up by Miss Stephanie Crawford and members of the black community in Maycomb. She recalls that Boo was always respectful and courteous to her when he was a boy. No matter what anyone said about him, Miss Maudie contends he always "spoke as nicely as he knew how."
When Scout asks Miss Maudie whether she thinks Boo is "crazy," Miss Maudie maintains that Boo isn't. Miss Maudie asserts that Boo has had a hard life; her comments hint at the fact that Boo's family life has been rather dysfunctional. She tells Scout she believes Boo lives in a "sad house" and that no one really knows "what happens in houses behind closed doors."