When people say that God spoke to them, or that they were called by God to do something, what do they mean exactly?

1. How did they know it was God speaking? Did God named himself? Could it be someone or something impersonating God?
2. Was the person always alone when God spoke to them? If a loud voice came from the ceiling or the sky, surely someone else heard it too. If so, did the other person understand the same message?
3. If the person was not alone in the room at the time but no one else heard the voice, how can the person be sure it was not a self-created voice inside their head, caused by a mental disorder?
4. If the voice was not from inside their head, how could they tell it was from God and not from a prankster with a megaphone?
5. Was the message always in a language the person could understand?
6. Did they know the meaning of all the words spoken by God?
7. How was the voice? Was it angry, detached, quiet, out of breath, menacing, or encouraging?
8. Was the voice speaking with an accent?
9. Was the voice male, female or something else?
10. Was it the voice of a baby, a child, an adult, an old person, or something somehow ageless?
11. Was it whispering, quiet, regular conversation level, loud or screaming?
12. Was the message an order,  advice, or information?
13. Did God speak to them more than once? If so, was it the same voice with the same characteristics?