It is demonstrable that at least some religions are made by men, and at least some teachings of all religions are made by men. What is not demonstrable is that all religions and all their teachings are made by men.
Obviously, you can’t trust something just because some religion says so.
But that is not why most people believe in things of religion.
Inspiration = the divine breath
God speaks to people.
We can’t. You should simply accept such things. You need to question and think things through.
But here is a rule of thumb: If something suits a particular function then it is likely made for that function. In the case of religion, if it is effective for power and manipulation of people then it is likely made for that purpose – those sorts of things are at least less likely to have come from God and more likely to have come from men. Teachings which puts all the power in the hands of God and the individual don’t fit this purpose of using religion for power over others.