Kilburn Hall (see below) does not just write dolphin books. He writes other sequels. Lots of indie authors undersell themselves, but KH is selling books for people who 'don’t give a crap about price. They want QUALITY!' As his blog explains (I have copied and pasted):
I’m not an Indie Author. I’m an author, and I’m not selling books.
I’m selling Kilburn Hall books.
No one else can do that! When you purchase a Kilburn Hall book, you’re getting the quality of writer’s like James Hilton, Trevanian, Vera Caspary, Robert Merle, Tony Hillerman, Robert Heinlein and my mentor, MIchael Criichton who invented the “techno-thriller genre.” All my books are written in the tradition of these outstanding authors.