CONTRARY to popular belief, the rise in luxury car thefts in the territory is bad for business at Jardine International Motor Holdings, Hongkong's sole supplier of Mercedes-Benz. Local car thieves have developed what appears to be an insatiable appetite for Mercs. Their penchant for the new S-Class Mercedes launched last year, with an average price tag of $1.3 million, put Mercs at the top of the car theft rankings by make. The recovery rates of these cars from the mainland is small compared with the total that disappear from Hongkong's streets and car parks at the rate of about three a day. In 1991 only 244 Mercs disappeared from their parking spaces without their owners' authorisation. Last year, of the 6,198 cars stolen in the territory, 16.5 per cent, 1,025, were Mercedes-Benz. This figure represents 16 per cent of all new Mercedes sold last year and is almost equal to the total number of Mercedes registered in Hongkong in 1993 to date. Company managing director Anthony Nightingale said: ''It would be difficult to measure accurately the impact on our sales, but certainly in the last quarter of last year we did see car thefts dampening sales potential.'' Finance director Peter Beynon said: ''The problem is the rising numbers of these cars being stolen has increased insurance premiums quite considerably.''