I've stated this before, but I would avoid buying any high end used acoustic guitar over the Internet unless there is a no questions asked return policy. Not because you'll get ripped off so much, but because I think there is a huge difference in tonality between identical models depending on how the wood has aged, how the guitar was stored, in what climate, etc. When buying used acoustics, I think having the opportunity to play it first is key. If you have a shop within driving distance that sells used Taylors, I would go there periodically and play every guitar they have within your price range until you find the one that has the tone and playability you want. You'll end up with a used guitar that sounds light years better than if you had bought new. But it requires patience and effort. What you are doing at guitar center is great. But not sure whether they have enough of a used Taylor selection.
Electric guitars are a different story.