I mean that if you're going to believe half of what's in a sutta, it has to mostly be based on faith. It can't be empirically confirmed that rebirth, bodhisattvas, enlightenment, etc. are real.
Can you confirm there are quasars without a telescope? No.
So you need to refine your apparatus. Train your mind.
And then you will say 'yes, I will train my mind and if I discover that there are other realms (as an example), how will I show them to you?'. The answer is that you won't. But you can't show me that you are thinking of an apple if I ask you, can you? Does that mean you can't think of an apple?
At the beginning one should consider theory like working hypothesis and suspend doubt. Let's find out if it is really as Buddha said. We train our mind and find out. If, OTOH, we negate it from the start, having no confidence at all, then probably we won't even bother. It's easier to negate what isn't apparent, but had we always done that and we would still be thinking the Earth was flat.
At the beginning how do we build trust? We study. If what is said is in accordance with our experience, if it makes sense and is helpful, then that's a good start. There are subjects not easy to investigate when we start, like rebirth, karma and other realms. So we don't need to believe these things blindly. Perhaps first it is wiser to investigate the ontological state of things we believe to exist. Then we will see that this world and this self we assumed were so real aren't that real after all. And we proceed from there. Negating things before knowing for sure has a reason, and usually that reason is our belief in a competing metaphysics, generally incompatible with Buddhadharma. But if we take the time to separate what are facts and what are beliefs, the belief for instance that consciousness is annihilated after death or the belief that there is an independent physical reality out there, we may realize that we know less that we thought we knew.
The problem is that we take for granted things that aren't more than assumptions, inferences and so on. Buddhadharma presents an alternative and if we are interested and have the capacity for it, we should put it to the test. But to honestly put it to the test, we can't judge it under the dictates of an alien paradigm that is erected over subtle, yet deeply rooted, metaphysical assumptions for the simple fact that such paradigm may be inadequate. Neither can we judge it without going through the training that is said to be necessary to verify it. This if we want to be honest. If we want to be simpletons, we negate all that seems strange from the start, trust in whatever is more common in our culture and lay our investigation to rest. But then we shouldn't be surprised if others who are going through the proper training don't take us seriously. Come on... it's like being surprised when seeing an astrophysicist not taking seriously the critics made to his conclusions by an overconfident undergraduate.