The Mystery on October Road by Alison Cragin Herzig and Jane Lawrence Mali, 1991.
A strange man has moved next door to Casey. He always wears a bandana tied across the lower part of his face, like a bandit. His pets are the strangest dogs Casey has ever seen, huge Irish Wolfhounds. He’s started fixing up his new house, but for some reason, he only likes to work at night.
One day Casey and her friend Cats (really, they’re both named Catherine, but they each have nicknames) go to take the man some bread that Casey’s mother baked, and they’re frightened away by one of the dogs. Casey goes back to get the bread they left behind, and the man tells her to go away and leave him alone.
Casey and her friends (Cats and Benny, a boy Cats likes) are curious about this strange man. They even wonder if he could be some kind of gangster, hiding out. At her friends’ urging, they sneak into his house one day to look around. When the man comes back unexpectedly, her friends get away in time, but Casey falls and hurts her ankle. The man finds her in his house, and she learns the truth about him.
The man isn’t a bad guy, and Casey even becomes a friend for him. The story ends on Halloween, when the man creates a special Halloween display for Casey of beautifully carved pumpkins. The part that always fascinated me was the way he carved them, by peeling the skin off the pumpkin and only leaving it in places where he wanted dark lines.
Part of the story is about how appearances can be deceptive. The stranger is actually a good person, but he is physically disfigured, which is why he doesn’t like people to see him. For part of the story, Cats isn’t really a very good friend for Casey, neglecting her feelings and the feelings of the mysterious stranger in order to impress Benny. But later, when she realizes that Casey was right about the stranger and that she was really hurt in their little escapade, she shows that she can be a better friend, too.
The book is currently available online through Internet Archive.
The Talking Table Mystery by Georgess McHargue, 1977.

The Ghost on the Hill by Grace Maccarone, 1990.
When they reach the state park, Dennis Ten Foot Bridge, who is the last of his tribe, tells the students about his tribe, teaches them wilderness skills, and leads them in group activities. One evening, Joey goes out to practice some rowing on the lake by himself, and he sees what looks like a large ghost at the top of a hill However, everyone knows that Joey lies about a lot of things, so at first, no one believes him. At least, no one except Adam.
The Return of the Third-Grade Ghosthunters by Grace Maccarone, 1989.
They try to use scientific methods to study the haunting. They measure the placement of the furniture to see if anything moves while they’re out and sprinkle flour on the floor to get footprints. But, even though they watch carefully and don’t see anyone enter the bunk house, when they go inside, everything is a mess, and the flour doesn’t appear disturbed. Everyone else is about ready to admit that this one is a real ghost, but Adam has another theory.
The Haunting of Grade Three by Grace Maccarone, 1984.
Most of the group members are misfits in one way or another. Norma Hamburger is a shy girl, frequently teased about her last name. Debbie Clark is a talkative girl who’s really into science. Chuck Webber, Adam’s best friend, is the class clown, always telling stupid jokes (and one of the main people who teases Norma about her name). Danny Biddicker is strong and good at sports, but he worries that he’s not as smart as the others. Joey Baker feels overshadowed by his large family, so he tells tall tales to get attention. The other kids don’t understand and get annoyed with his lies. By working together, they not only learn the secret of Blackwell House, but they learn more about each other and become a real team and friends.
Wrapped in a Riddle by Sharon E. Heisel, 1993.
The Mystery at Fire Island by Hope Campbell, 1978.
The Green Book by Jill Paton Walsh, 1982.
The Treasure of Kilvarra by Elizabeth Baldwin Hazelton, 1974.
Without the amulet to protect her, Christie continues her search for the treasure. An accidental injury takes her to the place where it is hidden, but it’s a dangerous place. Caught in a terrible storm, the children explore an ancient stone tower. There, Christie sees the ghost of a long-dead monk, gesturing to her, begging her to follow him to the treasure that she seeks. The monk died protecting it, and it’s a very unexpected but wonderful treasure indeed. But, getting out of the place is going to be even more dangerous than getting in.