Lying on God

There really is absolutely nothing "new" under the sun. Religion is no exception either. Before the apostles, before Jesus Christ walked the earth, and even before the prophet Isaiah, God knew there would be people who would claim to speak for him. Catholics claim they are the true church. Islam claims the God of the Bible is really Allah and Muhammad is his prophet. Mormons claim another testament of Jesus Christ. Jehovah's Witness claim another gospel and the new world translation bible. Who one is telling the truth? Can they all be true? Was God in the dark on this or did He put in His word how anyone can know at anytime who speaks for Him and who doesn't? Is it possible to know for certain what comes from God and what does not?