The answer is: The first-edition tales influenced folklorists to trust one another to gather authentic tales of living conditions.
In the excerpt from "How the Grim Brothers Saved the Fairy Tale," the narrator concludes the paragraph by making reference to the feeling of shared trust the Grimm brothers established among folklorists in the nineteenth century. He or she also mentions that mutual trust marked an era and a standard for folklorists and fairy tales, which also deal with living conditions and the supernatural.