A man has allegedly been stabbed by a prospective buyer who came to his Adelaide home to purchase a mobile phone.
Police said the potential buyers, a man and a woman, arrived at the man's Enfield address at about 8:45pm on Sunday.
They alleged the woman took off with the phone before the man stabbed the victim when he tried to stop them from fleeing.
The victim, 35, was taken to the Royal Adelaide Hospital for treatment and police were alerted.
Police say the suspects are described as a man of African appearance, about 190 centimetres tall, with a very slim build and short black hair, and a woman of Caucasian appearance, 163cm tall, with a chubby build.
Crime scene investigators have examined the scene and investigations are continuing.
Police are calling on anyone with information to contact CrimeStoppers.
In a statement, police said whether using Facebook, Gumtree, eBay or any other online marketplace, buyers needed to consider their safety first.
They urged sellers to meet prospective buyers in a public place.
Man stabbed in the back in domestic incident
In a separate incident, a 72-year-old man was stabbed in the back at about 11.45pm on Sunday.
Emergency services were called to Brougham Place in North Adelaide and found the man in a unit block being assisted by a neighbour.
He was taken to the Royal Adelaide Hospital with non-life threatening injuries.
A 57-year-old woman, who lived at the same address the victim was found, was arrested.
Senior Constable Rebecca Stokes said she would likely face aggravated assault charges.
"We just want to reassure the local community there that this was not a random incident, this was a domestic incident and the people involved are known to each other," Senior Constable Stokes said.
"We also want to encourage anyone else experiencing domestic violence, please don't hesitate and contact police immediately."