Some of the world's biggest hotel booking sites have agreed to stop engaging in shady marketing tactics like pressure selling and misleading discounts following an investigation from the UK's consumer protection group.

Calling the outcome a victory for UK holidaymakers, the Competition and Markets Authority (CMA) has given sites like Expedia, Booking.com, Agoda, Hotels.com, ebookers and Trivago until Sept 1 to change their ways.

An investigation launched last year turned up unsavoury practices among online booking sites that included pressure selling and misleading omissions. What exactly is pressure selling?

If you've ever booked a hotel room in a rush, because the website told you hundreds of other people were looking at the same room, or because the site was giving the impression that hotels in the area were sold out, you very well may have been duped.

Now, hotels will have to make it clear that consumers may be searching for different dates and refrain from posting sold-out hotels within search results, a pressure tactic used to induce people to book more quickly.

Websites will also be required to disclose when search result rankings are influenced by commissions paid by the hotel to the site. Discounts and promotional deals that are posted must be relevant and available to the user's search, and all compulsory charges like taxes, booking or resort fees shown upfront.

Though the CMA stops short of calling the practices a breach of consumer law, the group said that if the changes are not made by Sept 1, they will consider taking further enforcement action. – AFP Relaxnews