How do I know which is which?

I think God's punishment clearly applies where you sin, disobey or rebel against Him.

The devil's doing could also be considered as God's punishment in some cases. For when we sin, disobey or rebel against God, we expose ourselves to attack from the devil.

Then, there's the middle where good things happen to bad people and bad things happen to good people. Do we call good happening to bad people, God rewarding them for their evil deeds? Do we call bad things happening to good people, the devil punishing them for their good deeds?

That is why I believe there's an afterlife where everyone will be finally and fully rewarded or punished. This life is not enough. Is the suicide of Hitler or the poisoning of Abacha enough punishment for the evils they committed while they lived? I don't think so.