Those not in the diamond trade might find it hard to understand why Emile Chayto, a Geneva dealer with more than 40 years of experience, gave $14 million worth of gems to a stranger who claimed to be the wife of the deceased president of the Congo — before she had paid him one penny.

Unfortunately for Chayto, she was not the widow of Mobutu Sese Seko. And her wire transfer never arrived.