Your default state should indeed be non-belief however the only good reason for that non-belief is that there's no explanation for ghosts. You shouldn't reject things you haven't 'seen' before because then you'll go through life being ignorant of a vast amount of true things and events. For example you have not seen Hydrogen being fused in the core of the sun, but because we have good reason to think that's how the sun generates so much heat we should still hold that position because it has good explanatory function.
When you say "cause" do you mean "reason"? If so then yes that is exactly why you shouldn't make the assumption.
No because I do not currently have the explanation for how the teapot got there.
Exactly, never believe something without the reason. There's zero reason to believe in ghosts and that is precisely why we shouldn't believe in them.