You have to be careful with valuations because there are different types. Unless you specify otherwise, the 'default' valuation will be an 'insurance valuation'.
An 'insurance valuation' will ALWAYS be more than the price you paid because it is based on replacing it with a like-for-like replacement in the event it should get lost or stolen. The price would obviously therefore be higher because a 'one-off' stone would have to be sourced (not 'bulk bought'), the item of jewellery would need to be replicated like-for-like as a one-off by a skilled silversmith/goldsmith, which would obviously come at a greater cost than a 'mass produced' design. They'd also need to factor in future inflation, whether an alternative stone is available on the market, etc.
This is EXACTLY why Gemporia tell people to get jewellery valuations, because they know full well that an insurance valuation will come in higher than at item is worth.
'Value / Valuation' does not mean 'Worth'.
Then there is a 'second-hand' valuation. This will give you a valuation of obtaining a similar ring from an auction or similar in the event that yours was lost or stolen. This is usually for designs where the stones are fairly common (for example, a Quartz cabochon), in a common shape (for example, round), in a common size (for example, 6mm round), in a fairly 'plain' setting with no fancy design work. This would usually be for an item of jewellery that you like - but aren't too particular about it being an identical replacement to your original item.
Then there are 'private sale' valuations. This is an assessment of value between trade price and retail price – usually a value that benefits the buyer and the seller, i.e. that seller benefits from realising a price above trade and the buyer pays a price below ‘retail’.
Then there are 'probate' valuations. This would apply to someone, for example, that has found a drawer of jewellery at their deceased nan's house and wants to sell it on - but has no idea of what to sell it for. This valuation would give a fair valuation on each items worth so that the family member can sell it on at a fair price - without fear of either over-charging and pricing people out of buying, or selling it too cheaply and potentially losing out on a lot of money.
If you want a valuation on its precise worth, then you'd need to specify as such. This is where you will be left disappointed because, unless the retailer has made a genuine mistake on their pricing, or they've sold it at a loss because they've had it a while and simply want it gone, they'll value its worth at much lower than it was bought for.
If a jeweller genuinely believed their jewellery was worth the retail price that they claim it could be worth, then they'd sell it at that. They're businesses - they exist to make money. Why would any sane person or businesses sell something for significantly less than it is worth (particularly a business that has had, or has, financial difficulties recently) out of the goodness of their heart? It just doesn't make sense.
In reality, your item is going to be worth less than even trade price. If their retail price is, say, £1000, and their trade price to buy it from their supplier or to make it themselves is £600, then they'll realistically offer somewhere around £400-£500.
The only way you'd ever make any money on jewellery is by having something that is GENUINELY rare (not Gemporia 'rare') and no longer obtainable. IF you had something like an original Russian Alexandrite, then there will be genuine demand for that stone and you'll be able to sell it at a reasonable profit.
If Gemporia genuinely believed that their gold tone Nilamani pieces are worth the ludicrous triple / quadruple figure prices they claim they've had them valued at, then they wouldn't be selling them to Tom, Dick and Harry at home for £30.