Flipping Diamond/Pearl Jewelry?

So I've noticed on Ebay that you can buy saltwater pearls for literally like $100 from China, but at fancy jewelry stores and auction houses, saltwater pearls cost at least $3,000 per strand. I assume that if the Chinese sellers were lying about the legitimacy of their pearls (for example, selling glass pearls instead of cultured saltwater pearls), then this would reflect in their reviews? But maybe not...I suspect many Chinese sellers lie or exaggerate the quality of their pearls, but some are genuine. The trouble is you won't even know who lies and who doesn't until you get the pearls appraised.

I've noticed the same thing with diamond jewelry, though, although I'm no expert at telling different grades, but to a lesser extent. A diamond tennis necklace sells on Ebay for about $4,000, but at auction houses and fancy stores will sell for $5,000+.

Has anyone else noticed this? And has anyone here actually tried flipping fine jewelry? Like buying in the bargain basement (Ebay, Craigslist, etc.) and selling to the big guys (fine jewelry auction houses, estate jewelry stores, etc. for example)?

It would take a lot of money/investment/risk to get started, especially in diamonds - you'd have to pay the $4,000 to get started with at least one item, then get it appraised to make sure it's real, then you risk the stores and auction houses not even taking the jewelry or lowballing you - but could it work? I could also be wrong on this, so correct me if you think I am...for example, the Ebay tennis necklaces could be very poor grade diamonds, and the diamonds in stores could be very high grade. I don't exactly know the difference, as I said before.

I think there is probably a bigger profit in pearls because stores will probably buy it for half of what they'll sell it for and auction houses will take a commission, and there's less of a profit margin in diamonds as far as I've seen...unless you know where to get diamonds dirt cheap.

Has anyone tried this? If so, how does it work?