Giant Killers: Many are like a good "B" film. Fun for a moment, but difficult to take seriously. It's no secret to the marketing department that we all love a good deal, whether it is or not.
China and Europe: Without saying the items sound good or not or whether they are built well or not; find out whether the manufacturer has a solid North American service center.
Exactly What You Want: Any good saleperson will be able to tell you exactly what you want. Whether it is accurate is another matter entirely. It is reasonable not to know exactly what you want. Life is for learning. Hence, I find it to be almost impossible to ascertain how an audio product will sound in my house without installing it in my house. I live in a large urban area and I don't know a single retailer who is willing to bring over 100 lbs of gear to demonstrate it in my home. Since most gear does not live up to its hype and I'd send most of it back to the store, it is not in the best interest of retailers to demo it at my home. Buying reputable gear on the used market from folks with good feedback at least gives you the opportunity to test drive gear in your home and minimize your losses.
Reputable gear: A lot of reputable gear is flawed. I'd rather learn the reviewer blew smoke up my bum at the used price than at the new price.
Wonderful gear: I've bought some used gear that really impressed me that I would not have given a go at the retail price.
Buying New: Another advantage to buying used, and a lot of manufacturers don't get this, is that it gives you the opportunity to buy new with confidence - and be satisfied - once you know exactly what you want. Experience also provides you with shopping leverege to get new stuff at proper prices.
My free advice, and you know what free advice is worth, is to try and hear a lot of gear. Go to CES or Rocky Mountain if you can. You will hear suppliers say that the rooms are bad and they probably are, but I've not heard anything that sounded bad at CES sound good somewhere else. I've heard stuff at CES that I liked that I never otherwise would have considered and I've heard "Giant Killers" that are "B" films. Vegas is pretty fun too.
IMHO retailers are fine for folks who value convenience over value or really being immersed in this hobby. Nothing wrong with that at all. The fact that you are here and asking about Giant Killers, to me, rules out buying new from retailers for now. (Factory direct with a generous right to return policy the possible exception.) IMHO of course. Jeff