Definately independent is the way to go. They’ll usually offer good advice and tell you the truth, yellow gold isn’t so fashionable these days and if you have diamonds that are “old cut” again you.ll get a lower value.
Get a few quotes, as you.ll find some offer x2 on the lower end of the market
We recently had some rings made by a guy in Leeds, a really nice guy with passion for mtb’ing got chatting about Santa Cruz lol..
Anyway he valued and cleaned up some old rings for my mum, a few of the rings had the old cut diamonds and he said they command a Lower price, although an insurance repacement will value them at replacement cost at new cut.
He offers to display rings and take a commission on the sale, which could be an option, I’m sure precious metal and diamond dealers all work in similiar fashion