I bought a ring and bracelet for my wife from a very reputable dealer for £10k in total. She had them valued 5 months later for insurance purposes - £6k for the ring, £16k for the bracelet. I may be a canny purchaser, but I'm not that good; I'd suggest there's a wide disparity between the insurance valuation and what you can achieve in an actual sale!
Re the trade price for sale, you might want to contact kevkojak on here, who can give you an honest view on the actual market value of your items.