The ad on OLX read: "Three weeks old iPhone 6 Plus on sale for just Rs 35,000."

"A great deal!" thought Mahabir Singh, a resident of Haryana.

He quickly called the Calcutta-based seller, was convinced the deal was a genuine one and transferred the agreed amount to the person's bank account after he had emailed details of the courier shipment.

When the promised shipment didn't reach him after four days, Haryana resident dialled the seller and found his phone switched off. The phone number provided in the mailed copy of the courier receipt turned out to be fudged.

On Wednesday, police arrested three youths in Calcutta, including a student of Class XII, for allegedly duping at least a dozen people online.

Rajat Bose, 27, was the first one to be picked up from a rented apartment near Calcutta airport. He gave the police the names and addresses of his alleged accomplices Suman Paul, 25, and Imran Mondal, 18. Imran, a student of Class XII in a Madhyamgram school, was arrested from his house in a housing complex in Doltala, off Jessore Road.

The police said the trio had put up the advertisement on OLX - a free online classifieds marketplace for used goods, including mobile phones, furniture, cars, motorcycles, cameras and property - in the first week of August.

Mahabir saw the advertisement soon after it was posted and called the number mentioned alongside the seller's username. Rajat answered the call and allegedly said that a financial emergency had forced him to put his new iPhone 6 Plus on sale. He claimed to have the original accessories and the bill mentioning a two-year insurance.

Mahabir was taken in by the offer of an iPhone 6 Plus (16 GB) that had been used for barely three weeks at almost half the market price of around Rs 65,000. "The complainant said Rajat asked him to transfer the cash to his Axis Bank account after the shipment was processed," said an officer at the cyber crime police station in Salt Lake.

The next day, the Haryana resident received a mail containing a scanned copy of the courier shipment details. "The receipt was a fake one. When the complainant called what he thought was the phone number of the courier company, it was answered by one of the accused. He told him that the order was ready to be shipped," the officer said.

Mahabir didn't suspect anything was wrong and transferred the money. It was when he called the Haryana office of the courier company whose fudged receipt the accused had sent that he realised he had been cheated.

"He came down to Calcutta on August 13 and lodged a complaint with us," the officer said.

The police first went to the Baguiati branch of Axis Bank to confirm details of the account to which Mahabir had transferred the money. Although Rajat no longer lived in the address in the bank records, the cops found out that he had withdrawn cash immediately from an ATM near the airport immediately after receiving money from Mahabir.

The police verified the ATM location and transaction details, tracked the phone numbers used by the accused and contacted OLX for the IP addresses through which the fake profile had been used.

A CPU, a laptop, three mobile phones, a pendrive, at least 30 SIM cards, a passbook of Axis Bank and a debit card were found on the accused. The trio were produced in a Salt Lake court on Thursday and remanded in police custody for five days.

Officials of OLX, which has city-specific listings, couldn't be contacted for comment.

Has anyone attempted to cheat you online? Tell ttmetro@abpmail.com