I'm with West. Here's a bit I sent to the D-25 thread in this same "Acoustic/Acoustic-Electric" group on this same board:
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From my own experience (I've traded about 26 guitars through eBay in the last few years), you need to have confidence in 4 things for a sucessful transaction;
1: the quality of the instrument - if you're buying a guitar that has a good reputation (for me, that means Guild), and if you've done your reearch about the models and relative prices, then you should be reasonably confident, assuming full disclosure from the seller, you'll get predictable value. I don't think that a D-25 from a particular period at Guild is likely to be TOO dramatically different from another D-25 at the same period, although of course there are subtle and not-so-subtle differences that you'll only know with a guitar in hand. Get hold of Hans Moust's wonderful book, and you'll know all there is to know about Guilds up to 1977, survey the posts on this board and on Fender Forum - Guilds and you'll get a ton of more recent info.
2: the quality of the seller - feedback does tell tales. More important (for me) is the quality of conversation I set up with every seller. I've bought only one eBay guitar without at least some chatter with the seller, and that was not a good move. Ask lots of questions, ask for more photos, inquire about eveything that's not disclosed in the listing - in addition to the information, you'll rapidly get a sense of the kind of person you're dealing with. Like any business deal, that's the single most valuable piece of information.
3: use Paypal for your transaction. If you get completely burned, you'll get almost all your money back. It works.
4: be sure that you have an approval period and right to return if not satisfactory. You'll have to eat shipping both ways, so there's some risk there for sure. Don't allow sellers to give you "returns OK if the item is different from the listing" - all listings and write-ups are to some degree subjective, and an "invisible ding" to some is a major flaw to others, a "tiny crack in the finish" can turn out to be a major structural flaw that requires immediate repair, etc. The return policy needs to be clear - if you don't like it, you get to send it back. A savvy seller will also ask you to refund his/her eBay listing fee, but that's small potatoes.
I honestly believe that if you keep to these simple rules you have an extremely good chance of making a highly satisfactory deal. I've been truly burned only once (no conversation with the seller, and no shipment at all, see Paypal comments above). I know I'm sticking my neck out here, and that many of the folks on this board categorically refuse to buy a guitar unless they have a chance to play it. I completely understand that philosophy. On the other hand, because eBay does have some real and some perceived risks, the average prices on eBay are generally lower than they are in a retail store.
I'm sure there will be other comments, and not all in agreement. However you decide to get your first Guild, I wish you the best of success.