Question

Hallock ghost were live proposition how could he pen down ghost stories

Answer 1

John did not specialize in writing ghost stories but whenever an idea for a ghost story struck him, he would pen them down. Later, Helen, the female ghost told him that, "The Writer's Inspiration Bureau " used to help writers who did not have ideas to write ghost stories.  

Answer 2

John was not a specialist in ghost stories but suddenly every time an idea would come up mysteriously to his mind and he would write a story. Helen told him that it was the writers inspiration bureau which help writers who were without ideas and had soft mind on what to write.