"If you're asking if there's some kind of equivalent to the Kelly blue book for car values, sorry but no. The selling and buying of used body jewelry would be a private transaction and the price would be based upon negotiation and agreement between buyer and seller. If you don't like the prices and she refuses to bring them down to the range you expect, you have the option to simply walk away. If you make a final offer and she decides it's not what she wants to get out of it, she also has the option to walk away from the deal.
However, MY first concern would be whether or not you even want to purchase used body jewelry in the first place, especially if it has a known scratch. Take a look at this article before you make any final decisions/purchases: Is Used Body Jewelry Safe?