Fears of bogus tip-offs have forced Customs officials to place strict controls on a new reward scheme to combat spiralling illegal diesel use. Concerns were raised after oil companies pumped $1 million into the programme which rewards people who give information about the contraband market. Customs and Excise department Assistant Commissioner Chik Wah-wai said yesterday more emphasis would be placed on arrests and charges before the pay-outs, ranging from $3,000 to $170,000, were made. 'If there is a reward on seizure without arrest, some people may buy some diesel oil and put it somewhere and tip us off and get the reward,' he said. The minimum seizure before a payout is made is 10,000 litres. The Government estimates $3.8 million in potential duties was lost to the black market last year. Some taxis and buses use cheaper marked oil whose use is prohibited outside industry.