A jeweller sold a fake engagement ring to a couple telling them the synthetic stone was a sapphire.
Dr David Spencer and his fiance Christina Beales only discovered the band was worth far less than they paid when they took it to another dealer.
The dealer also informed them the ring, which had been sold as 18 carat gold was hallmarked at the less valuable nine carat.
Former police officer Martin Davies, 40, admitted six offences under the Trade Descriptions Act when he appeared before Brighton magistrates yesterday.
Davies, who was manager of De Rigeuer in Union Street in The Lanes, Brighton, at the time of the sale was given a two-year conditional discharge and ordered to pay £300 costs.
The court heard how Dr Spencer and his wife-to-be travelled to the city from London to buy the sapphire and diamond cluster ring in October 2001.
Len Batten, prosecuting for the city council, said Davies had handed the couple a sales invoice and an insurance valuation document which stated the stone was a cornflower sapphire and the gold was 18 carat.
But in January last year when they visited a jeweller in Hatton Garden, London, they were informed it was not a natural sapphire but a synthetic stone.
They paid £875 for the ring and two gold bands. When they complained the shop returned their money.
Matthew Bagnall, defending, said Davies, who has no previous convictions, had not been dishonest.
He said: "He did not know it was a synthetic sapphire. It was purchased in good faith from a reputable dealer."
He said Davies had enhanced the ring with 18 carat gold and, with hindsight, should have had it re-hallmarked.
He said Davies had left the police service after taking early retirement on medical grounds as a result of violent incidents he had been involved in including the Brixton riots.
"The loss of his good character is of great significance to him. He is suffering from depression."
He said Davies was a partner in the business as well as having a personal relationship with the owner of the shop.
They had now parted and he has moved to Aldershot in Hampshire.
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