Which one is correct?
If I hadn't seen it with my own eyes, I would never believe it.
If I hadn't seen it with my own eyes, I wouldn't have believed it.

Question

Answer

The second one because it's a THIRD CONDITIONAL : IF + PAST PERFECT, WOULD + PAST INFINITIVE ( have + past participal). You use the third conditional when you express an impossible situation

Answer

The first sentence would be: If I hadn't seen it with my own eyes, I would never have believed it.
The second one is correct.

Answer

They mean exactly the same.  two slightly different ways of saying the same thing.

Answer

All are correct. Just different means.