The difference is that scientific claims that are well supported have a mountain of evidence for them. That’s why they’re well supported. The claim that God exists has nada evidence for it. Somebody saying “God exists“ is not evidence. If I say “Pluto exists,” that is not a mere assertion, because there is a mountain of evidence to support the claim.
The critical thing is that the evidence is universally available. No trust in others is required; No faith is needed. If you build your own sufficiently powerful telescope (so you know there are no tricks being pulled by those scammers in Big Astronomy), and look at the place where Pluto is alleged to be, you will see that Pluto is indeed there. And
anyone who does this will see Pluto, no matter how much, or how little, they believe that it exists.
The whole edifice of science is built on repeatability.
Anyone can test any claim in science (not least because science requires the publication of methods - detailed instructions on how to go about making the claimed observations for yourself); And anyone who tests a claim, and can show it to be false, becomes a hero of science.
The more well established a claim, the more the accolades for proving it wrong (or even just showing it not to be universally right). Einstein is celebrated because he knocked Newton off a perch he had occupied for three centuries.
Neither Einstein nor Newton expected to be able to get away with bald claims or hearsay; They made predictions that were testable, and challenged the world to test them. It took some very detailed and precise measurements of the movements of Mercury around the Sun (made by Eddington) to show that Einstein was right, and Newton was not. But while Eddington was the first to complete the test set by Einstein, he was far from the last, and
anyone who doubts (or indeed anyone who doesn't) can repeat the same tests, and
see for themselves.
If you trust in Einstein's work, you are backing the right horse; But you are doing the antithesis of science. Einstein isn't right because he's a genius; He's a genius because he is right, and because we can
all check for ourselves that he is right.
The scientific approach to Einstein is Eddington's approach - "That cannot possibly be right, let me check. OK, I checked, and it actually
is right. And I had some friends check my work, and then I had some mortal enemies re-check it. And it's
still right, because none of them failed to obtain the same result as I did".