A consumer watchdog has recommended the regulation of air-ticket agencies, and urged airlines to inform customers beforehand about over-bookings.

The Shanghai Commission of Consumers' Rights and Interests received more than 530 complaints about airline services last year, about 32 percent more than in 2006.

The commission said complaints related to "fake electronic air tickets" and customers being denied boarding due to over-booking.

It said some illegal agencies had issued fake ticket receipts, while others made bookings but then had the tickets refunded without the customers' knowledge.

For example, a consumer surnamed Liu believed he had booked a China Eastern Airlines flight from Shanghai to Lijiang, Yunnan Province, at the Shanghai Buyecheng Travel Service Co Ltd in September.

On September 11, he confirmed with the airline that his ticket had been booked properly, and that he had paid the fare to Buyecheng. On September 23, however, he found that his ticket was invalid.

After investigations, he discovered that the agency he used was an illegal company passing itself off as a Buyecheng agency.

The commission said authorities should close down all the "black air ticket agencies" and add anti-counterfeit markings to e-tickets.

Another consumer, who only defined himself as Gala, said he was denied boarding on a flight from Shanghai to Bangkok because of over-booking by Air India. He failed to get any explanation from the airline.

The commission said authorities should establish a compensation system for passengers who are denied boarding. Commission officials said some airlines had their own compensation systems, but consumers believed them to be unfair.