All a priori knowledge we have discovered so far, is universal at least to the locality that we can see.

That doesn't matter.

Perhaps not. How would you presume that a "mundane" person tell the difference between genuine a priori knowledge held by a "special" person, and the rantings of a supposed prophet?

edit:

This should not be taken that I'm implying that believers are ranting prophets. Just a query as to how you propose to tell the difference.

I wouldn't. If is knowledge is truly a priori, and you truly didn't have it, there would be no way that you could know.

My advice would be to look at the person. If the man seems rational and honest, then maybe there is something to it. Then again, maybe not. It's really up to you.

Can a person seem rational and honest while discussing special knowledge they have that is neither experiencable or verifiable?

What seems rational and honest is based more on your prejudices than anything else. Ultimately, who and what you choose to believe is up to you. If you choose to restrict yourself to only what can verified without assumptions, you will end up with solipsism. If you choose to believe everything that comes your way, you will end up very confused. If you find some arbitrary 'halfway' heuristic, then you'll probably be better off. Just never forget that it is a heuristic that you are using as a criterion, or else your belief will be just as arbitrary as those who wait for alien spaceships to take them to bliss.

Really, its arbitrary. Just make up your mind.