Irvine Police said Arnold Min Baek, 27, allegedly posted items for sale online, agreed to cash transactions before meeting the victims, then robbed them.
On January 16, a Monterey Park couple was robbed at gunpoint of $15,000 cash when they met with Baek to purchase a 2008 Mercedes C300.
A La Habra Heights man was robbed at gunpoint of $4,200 when he met Baek to buy a Submariner Rolex on January 4.
Irvine detectives identified Baek through an online posting of a Mercedes for sale. He was located at a coffee shop in Lake Forest and arrested on Monday. Evidence was recovered, including a replica handgun similar to the gun described by the victims, according to police.
Police said Baek arranged to meet the victims at a residence in an upscale neighborhood, where he would come out from the side of the house. He would attempt to lure them into driving him somewhere.
Baek used photos of items pulled from public online sources, police said, and got the victims to agree to a cash price before meeting them. He told the victims he needed the money because he had a child with special needs.
Police advised people conducting online transactions to always meet in a well-populated public place, inform others beforehand of the interaction, to carry a cellphone, and not to carry large amounts of cash.