Hi and welcome to eBid.
As a jewelry seller, I list under costume jewelry all jewelry that isn't made with precious metals or stones, as Sarah Cov, Coro, other designer/non-designer jewels made from goldtone/silvertone metals, aluminum, silverplated, jewelry with rhinestones, glass, paste and plastic stones, etc.. I also list sterling silver under costume jewelry, (some might disagree with this, but it's a personal choice); IMHO fine jewelry is reserved for gold, platinum and gemstone jewelry.
Just my 2 cents.
Best wishes for many sales to all,