God doesn't lie because he says so.

[Cato]

But like the OP says: Why should we believe that God doesn't lie? Because he says so?

We shouldn't because god has lied according to the bible. God's prescription for leprosy in LV is wrong. God either lied or did not know the cure for leprosy. Theists can't stomach the latter even though the passages just before suggest that the same god thought houses could have leprosy.

What comes next is the typical theist mental masturbation that conflates lying with deception ignoring the fact that if there was intended deceit, which can't be proved, the lie was its mechansim.

This quickly degenerates into a barrage of bible spam claiming that god doesn't lie; which, is nothing more than the tired argument you alluded to: "because he said so".