1840, you'll be a "forum lurker" soon, just a few more posts to go
It sounds like you
do have a place to go "
where things are more likely to be what I am looking for without so much to go through to find the real stuff" and it sounds like that place is a jewelry store. Great! And I think that buyers will establish relationships with sellers who offer whatever they are looking for, 100% gold jewelry or Citroen oil filters, once they have made a purchase or two, and the seller has proven their mettle. This is the case for online shops as well as brick-and-mortar shops, and I'm sure you will strive to provide your ebid buyers with a high quality experience.
I'm equally sure that Gazza and Mark know how the categories are laid out on the other side, and want to provide the clearest selection of categories here while retaining some ebid brand identification, and the flavour of their non-American origin. I wouldn't think they would want to simply re-create the categories that exist elsewhere. With the lack of globally-accepted jewelry definitions, would it make sense for them to stick closer to the definitions common in the UK? And offer a glossary or educational page for buyers and sellers that lines out what can be found in each category, so we know where we stand? This would allow the seller to know where to place their listing, and to report those who are incorrectly listed. The buyer would be able to quickly review the menu of categories and begin their search in what seems the most fertile ground. I would still caution against too many categories, but presumably "fine jewelry" items would command a greater price and could be listed with a subtitle to further support their purity, hallmark, grooviness, etc.