I asked eBay :"Can you please clear up a problem for me? - is gold plated silver jewellery supposed to be in Fine Jewellery??"

I just received a response from eBay which says:

"I  understand that you want to be sure on the category to be compliant with our policy.

xxxxxx,  for gold plated jewelries, the correct category should be Fashion Jewelry. We intend to make Fine Jewelry category a category for 100% authentic stones or metals. This means that, plated, simulated, man made and synthetic jewelries should not be listed in this category.

I know this answers your question."

So, from the horses mouth.