Mr Michael Rigby, 30, an exhibition specialist from Oregon who comes here regularly for work, said: 'It was more than what it would have cost us at a restaurant in the hotel.'

He said that when he asked the stallholder whether the bill had a mistake, he only got a shrug in reply. Seconds later, the man returned with four others, who he said looked to be in their 40s and well-built.

He said: 'I guess they didn't want us to leave without paying.'

Ironically, he and his wife, Dewi, 36, had set out to show their friends - Mr Sal Rubio, 53, his wife, daughter and son-in-law, all here for the first time - how safe, clean and honest this island city was.

The food centre was crowded then, so when the helpers from stall 43, Tanglin Best BBQ Seafood, showed them to a table, they felt obliged to order from them.

Besides tiger prawns, they had four crabs, baby squids, half a steamed chicken, four bottles of beer and fruit juices.

Mrs Rigby, referring to the price of the prawns, said: 'They were prawns. It was not like we dined on lobsters!'

She added that halfway through the meal, the stallholder even plonked two grilled sting rays on their table.

'We told them that we did not order them and they were quickly taken away. Afraid we would be charged for them, we asked for an itemised bill. When it came, we were shocked,' she said.

Mr Rubio, who is from Arizona, told The Straits Times that the prices seemed comparable to those of an American restaurant and thought nothing of it - until Mr Rigby queried the bill.

Read the full story in today's edition of The Straits Times.