Can we be 100% sure there is/isn't a God?

No.There is no way of knowing whether or not there actually
is a god or gods.At best we can make some assumptions about what the world
should be like if there is/isn't a god (of any kind or faith)
and see if observations match our assumptions.But our assumptions are likely to be wildly inaccurate in this
case since none of us know the true nature of any god(s).

I thought in science that the opposite was the assumption.That is that we cannot ever proove something, but we can
refute things (i.e. disproove).In your example about Mickey, all that is required is for
some experiments to examine your brain activity, the energy
fluctuations around your body, perhaps some other things,
and we could potentially rule out that any signals where
being transmitted to your body ... that would disproove the
proposition.We could also investigate the liklihood that any Mouse
exists whose name is mickey and is capable of sending
signals.Science assumes that confidence in something is increased
if the predictions made based upon a theory cannot be
refuted, surely.

I would have thought in logic that one can prove
or disprove something given sufficient data and
validated assumptions.In science one does not generally speak of proof, but
of weight of supporting evidence.In my suggestions for investigating you Mickey Mouse
claim you'll notice that I advocated an investigation
of the source (mice named Mickey), the route (the signals),
and the destination (your brain).If we cannot locate any support for your claim in any of those
investigations then weight of evidence points to the
proposition being untrue ... but that doesn't mean it's
been proved absolutely one way or another.If, for example, no evidence at all is found then we can say nothing
regrading the proposition. Absence of evidence is not
evidence of absence.But this is all beside the point ... I spoke to Mickey
and he assures me that it's not him

Oh!!!I think I have been suffering from 'lack-of-agreement'
syndrome too

I am not making an assupmtion on an assuption,
but a reasoned suggestion that, since none of us
do know the nature of any god or gods, that we are not
in a position to make any validated assumptions in the
first place.If the liklihood of an assumption being spot on and of
being completely wrong are the same we cannot operate
with that assumption with any degree of confidence.