The group-buying website Groupon has had a number of complaints about its adverts upheld by the advertising watchdog, the Advertising Standards Authority (ASA).
Banners on its site promising discounted flowers, meals and travel did not actually allow items to be bought for prices advertised.
Groupon said the problem lay with its German arm, which created the ads.
The ASA has upheld similar complaints about the company in the past.
Groupon works by daily offering members discounts from up to 90% on items ranging from meals out and beauty treatments to flying lessons.
The offers are typically available for a set period and for a limited number of buyers.
Two internet banner ads promised "all you can eat in London for £3" and "XXL - Bouquet of Flower in London" showing a price tag which stated "from £8".
Both these, and three other adverts, invited consumers to click through.
Members of the public and rival companies challenged whether the offers were genuine, because when they clicked on the ads and subscribed to the Groupon scheme, they were unable to find any such offers.
The ASA said that Groupon had not provided evidence that the offers were available or that they had been taken up by consumers.
A spokesman for Groupon said: "This problem arose because our banner adverts are produced in Germany, where online regulations differ to the UK.
"In order to prevent this issue from arising again, all of our ad designers are being trained in the new UK code."
It said that all future adverts would in future be specific to the UK market, and their content would reflect whether they related to current, past or upcoming deals.
The ASA welcomed Groupon's response, but said the advertisements must not appear again in their current form.