"Trying" spirits and their message, and.what false spirits will never do. Here are some other additional tests(along with D&C Section 129) to understand if a messenger from the spirit world is/has been sent by Satan. These are biblical, and can be viewed through the link below at fairlatterdaysaints.org..
The teachings of Joseph Smith, the Book of Mormon, and teachings of apostles and prophets of The Church of Jesus Christ of Latter-day Saints affirm that Jesus is the Christ and that he "came in the flesh" as prophesied and affirmed in scripture. For Satan to inspire these latter-day truths goes counter to Christ's own teachings (Matthew 12:25–26; also Matthew 9:33–34; Mark 3:22–30; Luke 11:14–26; Jesus the Christ, pp. 265–266). https://www.fairlatterdaysaints.org/ans ... l_of_Satan
