Rakesh Mehta, his wife Manisha and Jitendra contacted Satyanarayan Mosun, who owns a jewellery showroom at MI Road, last month and said they were interested in doing business.
They also opened a firm named Mehta Investment and purchased some gold, making the required payment to win Mosun's trust, police said.
They placed an order of 4 kgs gold yesterday following which Mosun sent his son and employee with a gold bar weighing 4.1 kgs to Mehta's office in Shalimar complex.
The accused fraudulently replaced the gold bar with iron in the box in the name of checking weight, and left the office saying they were going to the bank to withdraw cash for payment.
The fraud came to light when his son checked the box and found the gold bar missing, police said, adding that a search operation has been launched to nab the accused.