I am slowly starting up a company ( slowed lately because shippit.com seems to have lost my package ) but my business model is that everything, or at least the greater majority, will be valued. Im using independent professionally qualified valuers.
Here in Australia the two main certified folks have the letters NCJV (national council of jewellery valuers, and AAJV (Australian Ass. of jewllery valuers. Yet legally I could value it for you lol and Im a noob…basically there are no laws covering valuations as far as I am aware. Valuations are opinions of who ever does it.
Replacement/insurance value is what you want. General rule of thumb for me is that an insurance valued item is about 25% over sale value.
Hope my opinion is of some value lol. I like the piece though 