a. the government: if they lie about what they provide you can sue them like you can any other business that defrauds you.
b. you can always just stop letting them access your account if you don’t trust them.
Nothing is fully guaranteed. Society as we know it could easily collapse in our lifetime. Ultimately it will likely be a less conditional income than a job where you can be fired at any time for literally no reason. I see a guarantee as a promise essentially. It is only as trustworthy as the party guarantying it.