I feel that this should be a person I've read more than one book by, so I won't say Stephenie Meyer, or Audrey Niffenegger, both of whom wrote books I didn't like. I want to think of someone I kept giving a chance to, and they kept letting me down.
I might have to nominate Laurell K. Hamilton, because I've read and enjoyed many of her books, but there have been plenty of books by her that are nothing but inconsistency and failure. Her relationship with criticism is just weird, I think editors stopped editing her work, and nothing gets proofed before print. That all makes me crazy.
Another possibility is David Weber. I have loved a lot of his books, but the more I read, the more disappointed I became in the way he's started to just pump out endless numbers of useless volumes.
James Patterson I've only tried once, but once was more than enough.
Really any of them qualify for this answer.
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