What a perplexing problem indeed! But there's a solution to that. Not to believe just anybody but you must seek for proofs and authority in those who claim to know or say the truth. Especially, that such lives are attuned to goodness, truth and love. Not just artificial words.
No wonder it's important to follow Jesus' words, after all, He is God and gave the proofs of divinity, not just in words but in deeds that only God could do. His miracles--curing the sick, raising the dead, healing the blind, the deaf and paralytics are motives of credibility. Plus His Resurrection from the dead, to top it all. What precisely did He say which may help us in our present quandary of the quest for truth, since everyone claims to be in the truth? Jesus tells this to us in Mt. 7:7 and He can't be wrong.
"Ask and it will be given to you; search, and you will find; knock and the door will be opened to you. For everyone who asks always receives; the one who searches always finds; the one who knocks will always have the door opened to him" (Mt. 7:7). Isn't it even an expression of common sense: "research will find a way." Everything, of course, depends on being true to oneself. Not diverting from one's true aim.