Around one in three online traders offered sales that were not as convenient as advertised on Black Friday last year, the EU said today, citing inspection results.
Consumer protection authorities in 23 EU states as well as Iceland and Norway screened "Black Friday" and "Cyber Monday" sales last November for compliance with European Union laws.
The sweep coordinated by the European Commission found many of the 314 online traders analysed to be wanting, Brussels said.
Some 30% incorrectly displayed discounts - in breach of EU rules stating that the reference price for a sale must be the lowest applied in the previous 30 days.
Almost 20% used pressure-selling techniques, such as countdown timers or claiming a product is running out - more than half of which were found to be misleading.
Another 10% used "drip pricing" - adding extra fees late in the purchasing process.
"A great bargain is no excuse to cheat the rules. Consumers expect a fair treatment, whether they are shopping online or offline," said the EU's tech chief, Henna Virkkunen.
National consumer authorities may take action against the businesses concerned, the EU said.
A US phenomenon, "Black Friday" sales have been increasingly adopted in Europe and beyond.
Held the day after the US Thanksgiving holiday to kick off shopping for the holiday gift-giving season, the sale is now followed by "Cyber Monday", which sees online shopping take centre stage, especially on electronics and other tech.
