Complaints about guest houses have more than doubled this year.
The Consumer Council received 45 complaints in the first 11 months, up from 21 for the same period last year.
Most complaints were about the lower end of the accommodation market, with problems arising from overbooking, overcharging and poor room quality.
Council chief executive Gilly Wong Fung-han said the number of visitors to the city had increased by more than 10 per cent this year. "In face of the mounting demand, some operators may run out of rooms and overcharge travellers," she said.
One of the complaints was filed by a German tourist, who made a full payment of €500 (HK$5,066) in advance for two weeks' accommodation at a guest house in Tsim Sha Tsui. When he arrived, he found the room had an awful smell, filthy bedding and no proper hot water supply. He did not stay.
The tourist's initial request for a refund was rejected, but with the council's help he managed to recoup half the cost of the unused room.
A Singaporean traveller - who visited the city in July - reserved a room at another guest house in Tsim Sha Tsui. When he arrived he was told the room had not yet been cleaned. He went out for dinner and returned at midnight, when he was told all rooms were full.
He was taken to a nearby guest house, which staff claimed was run by the same management - but that was not the case.
The tourist finally managed to get a refund of HK$680 - about 80 per cent of the room rate.
Council member Professor Ron Hui Shu-yuen said the trade descriptions law coming in next year would offer consumers more protection.