Christians believe that God can, did and does reveal himself through legitimate testimony* (and not just the testimony of the beauty of nature and the grandeur of the cosmos). And the Bible also tells us that there is an adversary who wants to dissuade belief and trust in God and excels in lies and counterfeits.
*He had been mentioned before as a relatively modern example, and it seems to me that it takes considerable denial to dismiss him casually and portray him as a self-deceived charlatan: