Although I will never do it, I accept comfortably that other people pick randomly from all over their decks after they have shuffled. The question I keep asking (and no one has answered yet) is that, if you are picking intuitively from all over the deck, why oh why do you waste time shuffling and cutting? Surely you would be guided to the right cards whether or not the deck is shuffled?
I suppose I'll answer, then. I don't pick "intuitively." I view the cards as inanimate objects that really can't "project" (or whatever term you prefer) their energy into the universe. It's also why I don't see decks as having personalities.
Anyways, to get back to the matter of picking from within the deck, what I do is fan out the cards. The ones that are fanned unevenly (for whatever reason) are the ones I usually end up choosing. I don't see this as the cards leading me to them, but rather the other way around: unconsciously, I'm
bringing the right cards to my attention. My arm/hand muscles are choosing the cards for me by making some of the cards more and less visible.
Because which card is in which spot when I fan the cards matters to some extent, shuffling and cutting still remains important.
Anyways! To address the issue of doubt about the Tarot...
Doubt is a natural part of life, so why shouldn't it extend to the Tarot? Especially because we are usually inquiring about things which cannot otherwise be known (other people's thoughts, the future, etc.); we have no certainties or guarantees about our interpretations. It all relies on your intuition about how "right" you are.
And the times when things don't go as you predicted? I see those times as learning experiences, primarily because, for whatever reason, we didn't think a particular card or set of cards could mean what they turned out to mean. Maybe we were inquiring about our career and didn't think emotional decisions would be associated with it. Now, we do, and we can look for those associations next time.
To get assurance that the card I chose is "right," I just try to think about how I conceptualize the Tarot. Any card can be relevant at any moment; the ones that appear are the ideas and aspects of life that I should pay some attention to. If you see the Tarot shuffling and cutting process as an exercise of randomness, then you can begin to stop feeling accountable for each card that's drawn. I'll admit, it's a total cop-out, but it works for me.
My suggestion for "re-doing" a reading is, instead of completely re-drawing cards for the same question with the same or another deck, hold the same question in mind and look for the same cards from another deck. Lay them out in the same pattern as the original (which you haven't put away, right? ^^), and compare them. Or, just look at the second deck. Sometimes, we can get different insights into a matter just by changing up the images on the cards.