How do I believe government word alone? I am not that simple minded a person?

For me word of mouth is the last thing I trust. Word of mouth is not considered evidence in court of law too. So how can word of mouth from POTUS be trusted? After all POTUS is human, not a God. Humans are not perfect. They lie, cheat, steal, and deceive. Its part of their DNA structure. Sure POTUS is considered a high standard person, but at the end of the day he needs to poop and fart too like all of us. OBL dead says Obama. How can i trust his word alone? Will a bank "trust" your word that you would pay back the loan? Will you trust me if I say lend me $500 and I will pay you back for sure? that's the exact problem i have with word of mouth. Blind trust is not my thing