[@Meta] First of all, nobody knows the nature of God. We can assume his nature by his interactions with humans and the actions of those humans carried on behalf of him, yes, but ultimately no one knows. And yes, it is better to assume that he is telling the truth but still no one knows that.

And this puzzles me, how is it more reasonable that he lies about heaven and not hell. From a purely objective perspective, imagining you are outside of the human race, what is the profit of torturing humans? They are just another sentient species, so do you get something of value when you torture them eternally? It yields no results. Saying that hell exists, even if it doesn't, is the same as it really existing since no one returns from the dead. Now, if the effect of just claiming that hell exists is the same as it actually existing, why bother making one?

Heaven on the other hand, is a place for the purest. I believe, if we say that God exists, that he devised earth as a test to find those with the purest spirit to stand beside him in heaven. Maybe we are already in "hell", our spirits failed the test and we are doomed to recycle our lives on this Earth. Maybe the test is already over and we are what remains.