Dene Athum, 19, was sentenced to a one-year community corrections order on Wednesday, after pleading guilty to the robbery at Derrimut on May 2 this year.

Melbourne Magistrates Court heard the victim agreed to pay $1200 for the iPhone he saw on the Gumtree ad placed by Athum, and agreed to meet to buy the item.

However, when the unwitting buyer turned up, he was confronted by Athum and his co-offenders, robbed and assaulted.

Magistrate Donna Bakos said Athum and others had approached the victim, before one of the offenders produced a wooden pole and demanded his money.

The victim was hit with the pole and fell to the ground, while the offenders ran off with his bag containing the money.

It's not alleged Athum knew of the weapon.

Later, a post on social media platform Snapchat showed Athum and a co-offender flaunting the victim's Gucci bag and hundred dollar notes.

The day after the assault, the victim noticed the Gumtree ad was still online and arranged to meet the seller in Derrimut.

He then passed on the details to police, who turned up and arrested Athum.

In a statement, the victim described his ordeal as traumatic and said he was now fearful of public places.

Ms Bakos took into account Athum's guilty plea and youth.

She said the robbery was planned and had a serious impact on the victim.

"I accept in your case you're sorry for what you've done," she said.

The court heard Athum has mental health issues and a mild intellectual disability, and his potential for reoffending depends on whether he keeps the same company.

Australian Associated Press