Permanent secretary Suwat Sidthilaw said yesterday after submitting the ministry's request for a probe to Tarit Pengdith, director-general of the DSI, that at least 20 tourists have filed complaints of being duped. The latest case was a Portuguese national who was fooled into buying fake jewellery from a Bangkok shop, so the DSI must take action against these daring con artists. He said the practice of selling overpriced products to foreign visitors was damaging to the jewellery business, which was a key source of income for the country, contributing Bt2 billion-Bt3 billion a year.