Corroborated as in two people both independently reporting the same evidence.
(Yeah, yeah, I know. Skeptics automatically gainsay this claiming "That's not evidence, they are mistaken, they are lying..")
Apparently God must be believed to be seen
Nope. People throughout history have experienced evidence for God that
caused their belief.
That's confirmation bias. If it's not then make these experiences available to skeptical minds.
Nope. Not confirmation bias.
...unless atheists are biased in the opposite direction.
Atheists say they don't think God exists because they say they haven't seen evidence.
The corollary of this would be that theists believe because they
have.