For the past four months, Google has been encouraging advertising agencies to create price comparison sites, which it presents in the Google Shopping box.
Google launched its Comparison Shopping Service (CSS) scheme in June 2018 in response to the European Commission's 2017 judgment, which fined the search giant a record-breaking €2.4 billion (£2.14bn), and ordered it to give its comparison shopping competitors "equal treatment".
Google approached advertising agencies and invited them to build comparison shopping sites.
It also offered substantial incentives to retailers to generate interest in the scheme.
The search firm then showed the names of the new sites under the images in its Google Shopping advertising insert, giving the impression of a thriving comparison shopping marketplace.
However, Google-certified operators told Sky News their sites were not designed to be used for shopping, with one calling it "an advertising system that looks like a price comparison".
As part of Google's CSS scheme, ad firm Shoptimised operates a site called High Street One, which at first glance resembles a traditional price comparison site.
Shoptimised co-founder, John Cave, said the site was never intended for consumers.
"High Street One is not designed for people to come on and shop," he said. "It's literally a website set up so people such as ourselves can pass on benefits to agencies and retailers."
Asked if that made the CSSs "fake", Mr Cave replied: "You could call them that, yes."
Richard Wyatt, managing director of another Google CSS partner, Onefeed, said his comparison shopping service was "a means of getting a rebate."
He added: "I don't think it's got anything to do with shopping sites for customers."
A Google spokesperson said: "Google Shopping complies with the European Commission's order – we give all comparison shopping services the same opportunity to show ads from merchants on Google's search results page as we give to Google shopping."
Since Google launched its comparison shopping service scheme, more than 90 sites have joined the scheme, with more than 60 in the United Kingdom.
Like High Street One, the majority are run by advertising firms, channelling advertisements from retailers into the Google Shopping box.
London-based agency Summit-Media, for instance, operates a CSS called Productcaster. Swedish search engine marketing firm Semtail runs a CSS called Shoptail.
There is no suggestion of wrongdoing but consumer experts have raised concerns that many of the Google-certified sites do not make it clear to users how they make their money.
"If you have a comparison site that's run by an advertising agency patently using only its clients, that's not even slightly a comparison site in any sense," says Jasmine Birtles, founder of Money Magpie, who also criticised the sites' rudimentary functionality, calling it "a nonsense".
Google has laid out some specifications for its partners, including offering "sorting or filtering" and a method of searching.
Yet Sky News found sites freezing or crashing, offering a small range of products (often including the most random items even in a targeted search).
Despite Google's stipulations, many also had no method of filtering.
The CSS scheme is Google's second attempt to foster diversity in its Google Shopping box.
In September 2017, three months after the commission's verdict, Google announced that it would allow rivals to bid against its own service in the auction for advertising slots on Google Shopping, the insert it shows at the top of product searches.
However, several companies with knowledge of the scheme told Sky News that take-up from price comparison sites was poor.
So, from June 2018, Google began approaching ad agencies and inviting them to build comparison shopping sites.
The search firm offered retailers a monthly rebate of £32,000 if they advertised through a CSS.
It also gave discounts of up to 20% on the rates of ads passed through a CSS, which one CSS operator told Sky News could be worth as much as £200,000 to large advertisers.
CSS operators could charge for access to their site, or ask clients to pay a management fee, for instance by taking a percentage of the rebate.
With demand from retailers high, some ad agencies also joined the scheme in order to keep existing clients.
"Our bigger customers were getting tapped up to go elsewhere," said Mr Wyatt from Onefeed.
"Realistically we were put in a position where we were forced to do it."
The quality and business model of the CSS sites could raise questions about Google's commitment to restoring a level playing field on its search engine.
"This isn't just brazenly non-compliant – Google have now reached the level of trying to circumvent the commission's guilty verdict," said Shivaun Raff, co-founder of Foundem, the company which is the lead complainant in the commission's case against Google.
Foundem has not taken part in Google's comparison shopping system, but the firm's other co-founder, Adam Raff, criticised its reliance on advertising.
"Everybody's just paying Google to appear," he said.
"Consumers aren't finding the best or cheapest products, they're finding the products from the merchants which are willing to pay the most."
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If Google fails to comply with the commission's decision, it would be liable for non-compliance payments of up to 5% of the average daily worldwide turnover of Alphabet, Google's parent company, backdated to the start of the non-compliance.
A commission spokesperson told Sky News: "We have not yet taken a position on whether Google has complied with our decision. And since we haven't done so, this obviously remains an open question."