1) Logically, either no religion is true, or one religion is true and the others are false.
2) Despite what logical positivists claim, there is no such thing as 100% total and absolute technical, clinical certainty about anything. I cannot "prove" that existence isn't some delusion in my own head, or that the universe did not pop into existence 5 minutes ago and that all my memories aren't fake, or that I'm not a "brain" in a vat-filled-with-nutrients and plugged into a computer program that I perceive to be reality.
3) Therefore, everything that everyone believes, we believe by faith. Everything. Everyone. The religious tend (for the most part) tend to be more honest about this than atheists, who still think the concept of "proof" has meaning.
4) Given 1, 2, and 3, the "true" religion would be the one that mends the broken hearts, heals the sick, feeds the hungry, houses the homeless, builds the schools and clinics and hospitals and universities and homeless shelters and soup kitchens, the one that sets addicts free from their addictions and slaves free from their slavemasters, the one that helps widows and orphans, the one that overthrows tyrants.
5) Historically, despite all its flaws and blemishes, only one religion does these things on a somewhat consistent basis.