I think there are two periods really:
1. The 'on-air' output started to go downhill around 10 years ago - when the likes of Scott Worsfold, Matt MacNamara, Rae Carpenter, etc all started leaving. Those knowledgeable and calm presenters were gradually replaced with the shouty, screeching 'stock phrase' and 'faux shock face' presenters that have contaminated the channel since. The days of being told how stones were mined, how stones form, their crystal structure, etc have been replaced with useless information such as "a huge amount of gold", "Fred from Ayrshire has bought 73", "Get as many as you can, absolutely" and repetitive prompts of "Christiano, show everyone how to buy" 53 times an hour.
Some genius within Gemporia even thought it would be a good idea to take a gamble with TV's village idiot, Peter Simon, at one point. Thankfully that was short lived.........
He'd fit right in now alongside Jess Foley and Lindsey Carr - but back in the days when their output was far superior and professional, adding Peter Simon to the line-up was ALWAYS going to end in disaster.
2. The final nail in the coffin was when Steve Bennett 'handed over' the company - and gormless Wagstaffe was brought in to run the channel. A guy that seems to have failed in the same role at JM and TJC previously. Add to that, Jake and Dave seemed to have far too much influence. The constant patronising and insulting viewers intelligence started, being told constantly that there's 'breaking news' in the industry for every gemstone known to mankind (a note to Gemporia - if you tell us that Dave Troth is on tomorrow with 'breaking news', then it's not 'breaking news' - it's simply 'news').
The jewellery production seemed to have been transferred to China rather than India, and the gold tone and gold plating crap started to flood the channel. The quality of the stones seems to have reduced significantly too - with poor and wonky cutting, windowed and/or fish-eyed stones, heavily included stones, and constant batches of treated stones that can still easily be obtained in untreated form - stones such as dyed Lapis Lazuli, reconstituted Jaspers, irradiated Morganite, etc. Even stones such as Smokey Quartz (irradiated) and Lemon Quartz (heat treated) have flooded the channel - despite being readily available naturally, and relatively cheaply.
No variety on the channel. Just endless amounts of filled Rubies, 'Nilamani', bleached Pearls, dyed or smoked Opals - and don't even get me started on the Jadeite! Years and years of endless Jadeite!
The amount of BS, deception and misleading went into overdrive too - with stones being sold under made up names (Serenite, Nilamani, Lehrite, etc), deceptive names ('Ruby Quartz'), stones being sold as something they're not ('Maw-Sit-Sit', 'Quartzite' and 'Serpentine' being sold as 'Jade'), telling us that coated Amber is a 'Wonder of Nature', a dyed Opal is a 'natural phenomenon', and dodgy price comparisons of fissure-filled 'purplish-red' Rubies set into gold tone silver being price compared against untreated pure red Rubies set into platinum elsewhere, etc. The list is endless.
In addition to all of that, their days of being a jewellery channel seemed to become less and less - instead flogging anything from illuminous yellow scarves, lipstick, slippers, candles, CBD products, perfume, glass monstrosities that were supposed to resemble birds, carvings that look cheap and tacky (but are anything but cheap), plant seeds, bird boxes, pills and potions, slimming products, bamboo Y-fronts, etc. Soon we've got menopause products on the way. Seriously? They're now coming across as a 'jack of all trades, master of none' version of eBay on TV - but with over-inflated prices and slower delivery. Up until 18 months ago, god forbid you needed to send anything back for a refund - you could have been waiting up to a month to get your money back, before Steve Bennett intervened again last year to resolve that problem.
I simply do not trust the channel, or its presenters, any more - and the prices of some items are EXTORTIONATE too.
Gemporia were never perfect under Steve Bennett. Lets not forget that 'Tulelei' (Mandarine Garnet) was sold under Steve Bennett. Steve Bennett himself also sailed a bit close to the wind at times with some of his spiel during sales pitches when he was presenting.
However, things were a lot more trustworthy and transparent. It was clear that some of the exaggerations were exactly that - whereas these days, some viewers could be easily misled by some of the BS far more easily because the likes of Troth waffling for an hour make it seem more convincing.
Everything just seems a bit 'desperate' and 'we want your money' these days. They come across as though they're simply 'treading water' and aiming for short term survival rather than looking like they want to restructure the channel to resolve the current issues and aim for long term survival.