Post History

> Are pieces routinely carbon dated (which would not show the true age given the time travel aspect)?

Carbon dating is irrelevant: it's used to date when a plant or animal was alive, because its metabolism exchanges carbon with the environment. Gold and silver don't contain more than negligible amounts of carbon; gemstones which have carbon in their makeup (diamond, jet, malachite, etc.) would have fixed their composition when they were created, not when they were polished, so there's no reason for anyone to try dating them. (Although if they did, 2000 years is less than the rounding error in the age of a natural gemstone).

> ... handwave away the idea that the buyers would think the sellers had done anything illegal ... Would the jewelry be thought to be replicas (worth more than ordinary modern jewelry, especially to a museum) or could they be thought to be the real thing (in impossibly excellent condition)?

If the buyers think that the artifacts are excellently preserved authentic 2000-year-old pieces and the sellers don't have documented provenance, they will think the sellers have acquired them illegally. Therefore to be consistent you require the buyers to think that the pieces are modern. But unless there are known period pieces which are almost identical, they wouldn't be replicas with particular value for a museum. The style of polishing of the stones would be extremely old-fashioned by modern standards, because knowledge about how to cut stones to enhance various properties is more recent than your period, so their best bet would be to sell them as "hyper-vintage" or "artisanal" on Etsy or similar.