Terror on Cemetery Hill by Drew Stevenson, 1996.
Halloween is coming, and spooky things are happening around Wilsonburg. Randall Davis, a new boy in town, comes to the diner looking for Sarah because he’s heard that she likes to investigate mysteries. Randall’s mother has recently become the caretaker of the cemetery, and Randall enjoys astronomy, so he decided one night to take his telescope up on top of Cemetery Hill. While he was there, he saw what looked like a hideous monster. Randall asks Sarah to have a look around the cemetery and help him figure out what he saw.
After some persuading, Sarah convinces Clark and Frog to come with her. Not only do they see the creature in the cemetery, but they find Mrs. Biddle, head of the town’s group of psychic investigators, unconscious in the Wilson family mausoleum. The Wilsons are the family that the town was named after. Mrs. Biddle and her group have been told before not to hold any ceremonies or investigations in the cemetery because they disturb people. She insists that she was investigating the creature in the cemetery and that it pushed her and knocked her out. Something strange is going on in the cemetery, but is it a creature come back from the dead, or maybe something to do with the recent bank robbery in town?
Everyone believes that the bank robbery was just one in a series of robberies staged across the country by a robber known as the Village Bandit because he tends to rob banks in small towns. However, Sarah has a different theory.
This is part of the Sarah Capshaw Mysteries series. It is currently available online through Internet Archive.
Toying With Danger by Drew Stevenson, 1993.
It seems that Sarah is right that someone is trying to spy on Dr. Becker. The kids learn more about the money involved in buying and selling toy designs when they visit the Too Wonderful toy company for a tour with Sarah’s grandfather. Making toys is serious business, and companies guard their designs very carefully. The Too Wonderful toy company wants to purchase some of Dr. Becker’s designs, but one of the members of the company says some strange things about Dr. Becker. Can the kids trust him? Can they trust the strange Dr. Becker? Can Sarah catch the spy before it’s too late?
One Ghost Too Many by Drew Stevenson, 1991.
Sarah persuades Clark and his friend “Frog” Fenniman to join her investigation of the house, but besides the resident ghost, they will also have to deal with a local group interested in psychic phenomena and a mysterious stranger who is paying the local bully to spy on the house.
Jumble Joan by Rose Impey, 1989.
The Flat Man by Rose Impey, 1988.
Scare Yourself to Sleep by Rose Impey, 1988.

The Mystery on October Road by Alison Cragin Herzig and Jane Lawrence Mali, 1991.
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.