TWO shop assistants who took their aggressive sales techniques too far when trying to sell a washing machine, were given suspended jail terms yesterday. Cheng Chun-keung, 25, and Chung Cheuk-kau, 32, even threatened to kill a customer, the District Court heard. The defendants were convicted of assault occasioning actual bodily harm, and each was sentenced to 12 months' imprisonment, suspended for two years. They had earlier been acquitted of blackmail and false imprisonment. Prosecutor Walter Lau alleged that on September 8, 1992, Cheng and Chung - of the Glorious Electrical Company in Queen's Road West - had threatened to kill customer Guo Donglin, 30, if he did not buy a more expensive washing machine than the one he had already handed over $1,280 for. Mr Guo was told that the cheaper machine was not available. Chung became hostile after Mr Guo asked for either a refund or the washing machine displayed in the shop. His colleague Cheng removed his shirt to reveal a tattoo of a dragon. Cheng later tried to drag Mr Guo upstairs, grabbing his neck, but Mr Guo put up a fierce struggle, biting Cheng on the arm. Out of fear, Mr Guo agreed to buy a washing machine for $3,500 and paid the balance of $2,200. Passing sentence, Judge Jackson said this was an unprovoked assault by two men in a shop where extremely dubious sales tactics were employed in the course of the transaction. While saying that the assault was ''not the most serious of its kind'', Judge Jackson said innocent customers must be protected from such outrageous behaviour.