Thanks for your question.
Every Evangelical/Pentecostal I have ever encountered tells me the same thing as the Chrisitian Scientists. When it comes right down to it, their beliefs are based on personal authority - they have been personally inspired to know that what they believe is true or their leaders are so inspired. I have had several who claimed that they have no use for Bible study and reading because they have a direct relationship to God through His spirit.
I have also met Mormon's who assured me that, if I were to pray with them, that God would reveal to me that Joseph Smith was a prophet sent from God and because of that revelatory experience I would know that what they believed was correct. These guys (the usual 2 "elders" just barely out of their teens) were utterly sincere but they were just as utterly mistaken.
I have heard exactly the same story from Seventh Day Adventists - just pray and you will be given the certainty that Mary Ellen White is a prophetess sent from God just like the Christian Scientists and their prophetess, Mary Baker Eddy. Not to mention the Bha'is and their prophet Baha'ullah. Some of the people from these groups had a detailed knowledge of their point of view. The Bha'i woman I spoke to for quite some time over a number of years was amazingly sincere but she was utterly convinced that her prophet was sent by God and that, through the spirit of the prophet, she was taught God's will. This person suffered severe persecution in her native Iran for her beliefs. Her sincerity was/is not in question. She was and is absolutely wrong.... just like the followers of Mary Baker Eddy and Christian Science.