Knives have to be one of the most faked ACW items, real ones bring a hefty price tag, so the counterfeit pieces come out of the woodwork. Online sites such as eBay make it easy for these ******** (my censorship) to sell to an unwitting public. Authentic reproductions of all kinds of accouterments, are being made for the re-enacting community and after years of service, may end up in an estate sale and on it passes……
Please stay off eBay until you know more, if not you will most likely end up with a pile of worthless junk. You'll want to trade up or sell at some juncture and get a very uncomfortable shock, ben there done that.
Go to every show you can, but don't buy anything as some of the online bandits are at shows. Find a group of trusted dealers and collectors, patronize them and learn. Buy research and reference books, they will save you countless dollars. The reference books actually go up in value far more quickly than the artifacts, when they invariably go out of print.
I just saw the "C.S. Richmond" by Davies go for $950; I believe I bought my copy for $95 from Davies at the Roots Conestoga Auction.