Travel firms have been warned to expect closer scrutiny of sales deals following a Which? investigation.

As the turn-of-year peaks began, the consumer watchdog published a report accusing several travel firms of using “psychological tricks” to convince people to grab deals before they expired.

But Which?’s probe last summer found some prices fell immediately after the sales period, potentially in breach of the Committee of Advertising Practice’s code.

Which? said it would continue to monitor the sector and sent its findings to trading standards and the Advertising Standards Authority.

Steve Dunne, chief executive of marketing consultancy Digital Drums, said: “Ten years ago, people would look at something once or twice. Today, they take the pulse of the market minute by minute.

“I would always urge companies to be as transparent as possible and if prices do fall, do a John Lewis and, within reason, offer to refund the difference if they find it cheaper.”

Dunne said constantly changing prices made it challenging for travel firms to meet customer expectations, but those that created unique deals would keep on the right side of the regulators.

“Travel is going to find this particularly challenging because there are so many moving parts,” he said. “You have to make the offer perishable, so it won’t be available after a certain date.

“I’d imagine Which? will look to highlight this every year. It’s great publicity for them.”

Stephen Mason, senior partner at Travlaw, said yield management by suppliers meant agents had to be aware of the “toxic mix” of fluid pricing and fixed-price deals.

“The industry needs to be careful of layering phrases like ‘special offer’ or ‘sale’ on deals when product is subject to fluctuating prices,” he said.

“Consumers are getting better at understanding that today’s price may not be tomorrow’s, or this morning’s may not be this afternoon’s.

“But there’s still a minority who fail to understand what everyone else does, or see some advantage in pretending not to understand.

“The big issue is when something is actively misleading.”

Mason said the issues Which? highlighted were not widespread in travel but warned it was an offence to offer a time-limited deal if you do not believe the price will rise.

Abta said “having accurate information at the time of booking, including transparency of prices, is really important” and “is reflected in our code of conduct”.

It added: “The number of complaints we receive each year about holiday pricing is very low, indicating that the majority of price advertising is trustworthy.”