The well-dressed man, thought to be of Middle Eastern origin, used sophisticated copies of American Express Gold Cards to steal £8000 worth of Asian works of art from JAN Fine Art in Kensington Church Street and £4500 worth of items from a gallery in Pimlico Road.
He visited JAN Fine Art on May 31 and spent around half an hour talking about the antiques and saying he was from Dubai. He was also speaking on his mobile telephone.
He used the fake AmEx card to buy an Imari group of a man and woman c.1700 worth around £3000 and three Chinese blue and white hookah vases from c.1700 standing between 53/4 to 9in (14.5-23cm) high.
The transaction was authorised by the handheld card-set. However, a week later Ms Shimizu of JAN Fine Art discovered that the transaction had failed after being blocked by the owner of the original card which had been cloned.
American Express told Ms Shimizu that they accepted no responsibility and would not offer a refund.
Police are investigating the matter and anyone with information should contact DC Hollywood at Kensington Police Station on 0208 246 9256, quoting crime reference 5611984/08.