I poise a question.

[FiniteImmortal]

Logically, God cannot be anything but good; he can't violate his own existence.

The question is, assuming this being 'God' exists, how do you know he's God?

The question you raised self-implodes on it self, because the context is invalid. Its like asking what happens when an unstoppable force hits an immovable object.

Strictly speaking (and ignoring the impossibility of those things given the way the world is), that "paradox" is solvable: The two things pass through each other. Thus, the Unstoppable Force isn't stopped and the Immovable Object isn't moved.

More to the point, you seemed to not have realized that no matter how you answer the question "Can God lie?" can be circumvented by a being who is omnipotent and omniscient. If the being who you call God shows up and says "I do not lie.", how do you know that's true, especially when given its capabilities it could easily fool you into thinking it doesn't.

Its like saying "God is all powerful and can do anything in existence, including not be ". God is bound by reality, just as we are. God cannot violate his own character or he would cease to be God. If God was "lying", such as us men do, then he couldn't be the standard for perfection and the absolute reference point for reality, as his infinite perfection would become finite an limited, and hence... not God.

You assume there is a being whom is the paradigm of goodness itself. That's just assuming what you're being asked to evidence.

God cannot be actually and wholly Evil. Evil cannot exist on its own, it can only exist as an aberration of good. This is actually the portrait scripture paints of Satan, who was once good but through his own freewill became corrupted and is called "the father of lies".

Not only is this an instance of you trying to shove your ethical ontology on us, but you're misunderstanding your own ontology. And this is a problem with Christian theology. Their ethical ontology is literally just a Platonism rip-off (in terms of how it's employed by apologists), they don't realize what that metaphysical view does to the rest of their metaphysics. Since under your view (which is an example of Platonist influence on Christian thought) ONLY God is good, you can't say anything else is good. They are just pale reflections of what is actually good on your view: God. So on your view, to say anything besides God is actually good is a contradiction in terms.

When I mention God, I hope it is clear I'm not referring to an invisible flying spaghetti monster, or Zeus, or any other arc-type construct of human kind, those invented transcendental gods (lower case) are obviously not contenders when trying to establish if there is a god or not, and trying to understand what conforms to reality as we know it.
I'm referring to the only God that could conceivably exist. It is between this God, or nothing at all, if we are to honest for a second. The God that could exist would have to still be anchored in reality, and not merely a magical wizard that waves his wand and makes cupcakes anytime he wants. If there is an infinite intelligence in our universe, he must be approached objectively and without silliness.
This God must needs have always existed; beyond time and space. It is far more likely that there should be nothing at all, no intelligence or self-awareness of intelligent life. If he exists eternally, and has infinite intelligence, and we are new creatures here, new to this life and we have the ability to conceptualize our existence, there must be a reason we are here and we know we are here.
When a finite being, such as a man, a fictional god story of zeus or other obvious man-made entities makes a statement, it is suspect. When a being that transcends us, (like the one infinite God) makes a statement, it is in a different context than that of a finite being's. The law of gravity can't lie, if the law of gravity had freedom to violate itself at will, the fabric of spacetime would have collapsed by now. Part of the description of gravitational phenomenon is that it is a certain way, and we rely on it being a certain way to travel to the moon without fail, we don't worry if its is going to drop us all of a sudden and without warning.
You are right, I'm framing the real God to be the measure and absolute standard of right and wrong; the horizon line and the only reference point to the universe. An attribute of who he is in his essence is goodness. As i said before, Duality, aka badness and goodness being equal but opposite forces doesn't stand to reason. Badness can't exist on its own, as goodness can. Badness is only goodness out of turn. You can't explain the normal from the deviant, you can explain the deviant form the normal. I think it is reasonable, that if this God exists (the only one worth entertaining and eligible for intelligent discussion), he is trustworthy in not violating his own existence. For him to do so would be supernatural and a form of wizardry I'm not familiar with.

I'm not trying to force any ontology on anyone, merely trying express my view of the question raised in the title of this thread.
Thanks for the reply.