THE soft drink vendor at Beijing's Temple of Heaven Park evidently thought he was dealing with just another dumb foreigner when he tried to cheat his customer out of three yuan (HK$4). However, this particular customer ended up costing the vendor three months wages and a major loss of face. The foreigner in question happened to be a European diplomat who was showing a couple of friends around the capital and was getting increasingly fed up with being ripped off at every stop. After a protracted argument, he decided the time had come for action and started taking photographs of the stall holder. The pictures were then passed on, along with a formal complaint, to the park authorities and within a few days the park's director appeared at the diplomat's embassy with the disgraced vendor in tow, bearing gifts and apologising profusely. The diplomat was informed that the vendor (a park employee) had been criticised and was to be docked three months' pay and that a notice would be put up in the park informing tourists of a telephone hotline service designed to handle similar complaints. While the response to the European diplomat's complaint may have been atypically accommodating, it is at least indicative of Beijing's determination to clamp down on the tourist cheats who, officials say, are damaging not only the capital's reputation asa tourist destination but are also jeopardising the city's chances of hosting the 2000 Olympics. Complaints from foreign tourists and visitors from China's provinces have increased significantly this summer, forcing the city government to take action. ''The situation in some places is getting out of control,'' a senior municipal government official said. ''It is now virtually impossible to visit any of Beijing's landmarks without getting cheated.'' The crackdown was formally launched last month and has so far netted ''several dozen'' cheats, the official said, adding that all visitors' complaints would be dealt with thoroughly. The biggest problem for the government at present is undoubtedly the band of small-scale one-day tour operators who take unsuspecting visitors from China's provinces around the major tourist sites outside the city. Many tour companies are unlicensed and privately run, use unroadworthy vehicles and only take their customers to shops and restaurants where they have a pre-existing financial arrangement with the establishment's owner. Tour guides will usually buy entrance tickets to places such as the Ming Tombs on behalf of their customers and then charge the tourists double or even treble the ticket's face value. And those who have refused to pay have often been threatened with physical violence by the tour guides or their drivers. It has become almost routine for soft drink vendors and souvenir sellers at well-known tourist sites to cheat their customers. Store holders usually charge outrageous prices - up to 30 yuan for a can of warm coke - but also short changing customers is commonplace, as is selling fake goods and taking photographs without any film in the camera. Taxi drivers are also getting on the band wagon by pouncing on bewildered travellers arriving at the airport or the railway station. An American tourist at the Beijing airport, for example, asked one of the drivers milling around the arrivals hall to take her to ''a hotel in Beijing'', which, after relieving her of US$20 (HK$155), he did. The only problem was that the hotel he took her to was two minutes from the airport and nearly an hour's drive from the city centre.