The jewelry community is small. Most conceal carry. It takes skill to break down pieces and sell them on. Jewelers stay aware of robberies, in case someone tries to sell a stolen item to them. It’s an honor system.
Discussion
Also frequently the more valuable items aren’t for the metal or gem quality alone but the skill or brand recognition of the maker.
Mostly true... melting metal doesn't require much skill. Just the right tools.
The jewelry community isn't that small.
Honor systems are the worst form of security.
Some jewelery artists don't really care where the material comes from.