Police arrested Pratheep Yodyeam at his home and charged him with fraud, according to Pol Lt Col Pramote Chanboonkaew, chief of Buppha Ram police station in Thon Buri.
The arrest followed a complaint lodged by two women to hours earlier, saying they were cheated by the 24-year-old man on an agreement to swap mobile phones.
The two women, whose names were withheld, said they found an advertisement on www.olx.co.th, a popular site hosting sales and swaps. They said Mr Pratheep posted an offer last month to sell second-hand iPhones 5s for 11,000 baht apiece.
They contacted him on his Line address mentioned at the Olx advertisement, and agreed to exchange a Samsung Galaxy Grand model for one of the used iPhones by mail.
The women said they mailed the Galaxy, and received from from Mr Pratheep a box with a rock inside.
They decided to locate his house according to the mailing address before going to the police station.
Mr Pratheep told police that the two women were his second victims. He had also sent a rock by mail to another costumer after the buyer transferred 12,600 baht in cash for the purchase.
He said he planned to sell the Samsung phone for 4,000 baht and would use the money to pay a debt owed by his grandmother.
Pol Capt Anand Sawangamporn, a chief investigator of the case, suspected he was lying to officers and urged customers cheated by Mr Pratheep to file a complaint at the police station.