How does science finds the truth. Not that accepting what some Einstein said as true. Scores, hundreds of people check things claimed. Scores, hundreds of laboratories engage in testing things claimed. What comes out true is then accepted.
But if you go just by faith and accept what some uneducated Iranian said a century and half ago without any evidence and claimed that he is a messenger of Allah, then it is your wish. Generally, people in 21st Century do not accept such things, I have nothing against that. But you might be an exception.
It is a typical Iranian thing. It is recorded that at the time of Iranian revolution, there were 1200 people in Iranian jails claiming that they were saviors, Mahdis.Common thought is the 'Argumentum ad populum'. Argumentum ad populum - Wikipedia
By personal experience and not by what someone says. When they see that injustice harms everyone.
How did Hindus arrive at the conclusion that the Bhagavad-Gita was truth? Apart from just believing in it?