Under an arrangement known as the “0+3” system, arrivals undergo three days of medical surveillance at home or in a hotel. They are free to move about the city but are barred from visiting places such as restaurants and bars.

One 35-year-old consumer said he paid about HK$35,000 (US$4,500) between September 30 and October 1 for six family members to fly on HK Express from Hong Kong to Tokyo. The family planned to be in the Japanese capital, a popular destination, from October 15 to 19.

But within 24 hours of the booking, he found the price for the same flight had dropped by nearly 30 per cent – from HK$5,630 to HK$4,110 per ticket – amounting to a difference of more than HK$9,100 in total for six tickets.

He filed several complaints to the airline’s customer service department but was eventually told fares fluctuated based on market conditions and seat availability. A refund would not be issued, he was told.

“I don’t mind if it’s a 10 per cent difference, but a 30 per cent difference is quite ridiculous,” said the consumer, an employee of a multinational corporation. “I think it’s a dishonest pricing system.”

He approached the Consumer Council but was told it could not help much because there were no laws governing such practices.

He noted that the United States had policies allowing consumers to cancel their reservation and receive a full refund without a penalty for 24 hours, but the city did not have the same rules.

Store manager Paul Yip, 41, said HK Express’ website timed out twice while he was buying eight adult-fare tickets to Phuket on September 30 – first for an hour and subsequently 30 minutes – forcing him to restart his purchases.

He said the prices for both leaving and returning tickets increased after the time out, but he purchased them and paid about HK$44,000 in total.

The returning tickets increased from HK$1,788 to HK$2,118 each after the website timed out, he added.

But Yip was shocked to find that returning tickets dropped to the original price within 12 hours after his purchase. With eight tickets, it amounted to a price difference of HK$4,720, he said.

He tried to approach customer service to refund the price difference but also in vain.

“I feel like I’ve been lied to. Prices can go up and down of their own free will without consequences. That is very unfair and not the way to do business,” Yip said.

“How is it right and fair that when you buy the tickets, they won’t let you until they raise the prices?”

A customer service officer reached out to Yip on Thursday afternoon, saying she would try to submit a request to higher-ups to refund the differences, but told him the request was likely to get rejected.

Another traveller in her 30s, who gave her name as Kathy, said the price of her one-way ticket from Hong Kong to Osaka increased by about HK$300 when she bought it on October 1. She had been monitoring the prices for a week before purchasing.

She ended up paying roughly HK$1,900. But the next morning, she discovered prices dropped by HK$1,000 to around HK$800, less than half of what she paid.

“It’s very disappointing even though I understand they are free to adjust the prices. But I was not expecting to suffer a HK$1,000 loss [for my] one-way ticket in only one day,” she said.

A spokeswoman from HK Express said the airline “continues to review the pricing of its flights based on the latest market conditions and seat availability”.

“As a low-cost carrier, all HK Express flights are non-refundable,” the representative added.

Last week, the carrier pledged to add more than 400 flights to destinations popular among Hongkongers in the coming three months.

This would lead to more than 80,000 additional seats up for grabs for those planning to fly to Tokyo, Osaka, Fukuoka, Bangkok and Singapore.

Since the “0+3” model was introduced, the Consumer Council had received two complaints relating to airfare cuts, a spokeswoman said.

“While the Consumer Council is not in a position to provide specific legal comments on specific cases, generally speaking, once both parties have entered into a contract, it should be regarded as effective and legally binding on them,” she said.

The representative added that Hong Kong is a free economy where traders can set and adjust their pricing according to the prevailing market situation.

When it comes to more volatile situations, the council advised consumers to compare prices closely and to review the terms and conditions carefully before entering into a contract, as “general situations might not be applicable”.