Police said each victim agreed to meet their attacker in the McDonald's restaurant car park on Telford Road, Edinburgh, believing it was a genuine buyer.
In all of the cases the people had posted an advert on the Gumtree website to sell Apple computers or phones.
Lothian and Borders Police said they were investigating whether the incidents were linked.
On Monday, a 24-year-old victim arranged to meet the suspect, who said he wished to buy an Apple computer. When they met, the victim was threatened and the man stole the item.
Last month, on January 20, a 31-year-old was wrestled to the ground by the suspect, who stole an iPhone that was for sale.
A 33-year-old was assaulted and an Apple computer stolen in similar circumstances the following day.
Inspector Mark Rennie said: "While no victims were injured, all were understandably distressed as a result of their respective ordeals. We are carrying out inquiries in order to establish whether these incidents are linked.
"At the same time we are warning anyone conducting any transaction over Gumtree or any similar website to take precautions to ensure their safety."