I would not believe much of what I read about Old Pawn in sellers descriptions on Ebay. I am sure some honest sellers make mistakes, but as I look at the auctions there I see the term applied to many indian jewelry items that are not Old Pawn. If you are going to pay market price for this kind of item, Ebay may be an interesting, if risky place to shop. Even if you know what you are doing the picture quality of the items shown for sale may not be sufficiently detailed to be certain of what you are bidding on.
We found that even in person it was extremely difficult to tell real from fake turquoise. The plastics industry has been very creative and unless you are a registered gemologist you just can't tell for certain that you are getting what you think you are.
One of the major characteristics of old pawn, which is easy to tell in person, is the pieces are heavy. They used a lot of silver in the old items, especially in Navajo work. It is interesting to see some sellers are beginning to include the weight of the piece in the auction.