TWO washing-machine salesmen who beat up a customer until he bought a more expensive model from them were convicted of assault yesterday. Cheng Chun-keung, 25, and Chung Cheuk-kau, 32, were found guilty in the District Court of assault occasioning actual bodily harm, but each not guilty of a blackmail and false imprisonment charge, in the District Court. They had denied the charges. During the case, the court heard that Cheng and Chung had threatened to kill Guo Donglin, 30, if he did not buy an expensive washing machine at the Glorious Electrical Company in Queen's Road West on September 8, 1992. Mr Guo had handed over $1,280 for a cheaper machine, and then paid another $2,200 for a more expensive one, the prosecution said. In his judgment, Judge Jackson said the two defendants and another person had lured Mr Guo in with a misleading and attractive advertisement. He accepted they had bullied and intimidated him into buying the more expensive machine. Cheng even had removed his shirt to reveal a tattoo of a dragon, he said. The judge said he believed the entirety of Mr Guo's evidence. However, he considered the charge of false imprisonment as ''misconceived'', and found himself unable to say that the particular circumstances of the case amounted to blackmail. Prosecutor Walter Lau had chosen to proceed with the blackmail charge after he was asked by Chung's defence counsel, Toby Jenkyn-Jones, in final submissions, whether the Crown would proceed with blackmail or the alternative charge of criminal intimidation. Earlier, Judge Jackson had admitted as evidence a statement by Cheng to police, but rejected Cheng's exculpatory account. ''It does give his [Cheng's] account of the modus operandi of this shop which, if accepted, gives an appalling state of affairs which every shop in Hong Kong should be aware of,'' he said. Cheng's statement had said the company priced appliances lower to attract customers. ''If any customer comes to buy electrical appliances, the salesman would make various excuses to increase a few times the price of the goods - that is to say, if a customer at a preliminary stage had already made a down payment for the purchase of a certain brand of electrical appliance,'' it said. ''Finally, the salesman will increase the price by using a certain reason or ask the customer to change the purchase to another brand of electrical appliance. ''If the customer refused, his or her down payment would be forfeited or the salesman would threaten the customer,'' it said. Sentencing was adjourned until April 26. to allow background reports on the defendants to be prepared. Cheng was represented by solicitor James Li.