I, the believer, get to define God.
Not completely, but I take what I have heard from my parents, my siblings, the kids in the neighborhood, and my Sunday School teachers, and I fashion a mental picture of God that may - or may not - resemble other concepts of God that others may have. Does my God-Concept match the one in the Bible? Maybe a little, but I’ll discover decades later the problem with that. Does my GC match the God of classical theism? You must be kidding! I won’t know what that is for another 30 or 40 years.
If and when I try to validate my GC against reality, you can imagine what I’ll come up with. If there’s a "Standard", mine won’t be it. Regardless of how far my God-Concept deviates from some norm, if I want to be justifiably confident of my GC, I should frame it as a hypothesis that can be compared against the real world to assess its validity.
As a bonus, developing a justificatory argument that defends my view of the proposition “God exists” prepares me to win hearts and change minds should I ever bring it out into public to debate a dissenter, and also helps me to identify gaps, weaknesses and outright flaws. Who knows, I might have to modify or discard some or all of my GC and adopt a new one that provides a better explanatory framework!
Now, where do I start? How can I test my God hypothesis against the real world to verify its plausibility? I’ll start with something accessible to me, like how often God answers prayers. Granted, this ability is not explicitly embodied in a “classical” definition of God, but seeing as how I don’t expect to see her, him, it as a physical person, the answering of prayers is the closest the lay person can get to detecting God's existence.
So ... I pray. And sometimes my prayers are answered - HALLELUJAH! But if I’m honest with myself, is it an expected result? Should I expect that a prayer is answered on occasion? Could there be a simpler explanation? Of course, so let’s try something tougher - let’s try praying for an amputee’s limb to be restored. And - as we know - this never happens. It. Never. Happens. So we have a negative result on our test of the hypothesis that God answers prayers. But there’s a snappy rejoinder to this disconfirmstion of God’s existence, the ever-useful “But God works in mysterious ways”. And the counter to that inane bit of apologia is that you’ve just declared God to be an unreliable subject for observation. Which means we can’t know anything about her. Which means we don’t know if God has our best interests in mind. Or which means we don’t know whether God is interested in us at all. Or which means God could be a trickster, or evil, or not there at all, because when we declare “But God works in mysterious ways”, we’ve pretty much ruled out any hope of doing more than speculating. So maybe we should shut up a while.
While there is lots more to be said here, I’ve summarized my initial thoughts on validating my (hypothetical) God-Concept. Keeping in mind the problems of reliability in going from a real-world occurrence to a human perception, to a human interpretation and eventual rationalization, you can see how many hurdles we face when trying to justify that the God that you (or I) believe to be real actually exists