Shaun Mark Gale is accused of aggravated robbery and is contesting the charge in the ACT Supreme Court.

The court on Tuesday heard that Mr Gale arranged for the complainant to meet him at a cul-de-sac on the evening of Anzac Day in 2021 after the latter advertised a Samsung Galaxy for sale on Facebook Marketplace.

Mr Gale had used a profile under a different name on the social media platform, telling the complainant he was buying the phone for his daughter who "really wants one tonight before she goes back to school".

At the meeting, Mr Gale arrived on a bicycle and handed over a wallet.

He then allegedly produced a gun, pointed it at the complainant then threatened to shoot and demanded that the phone be handed over.

Mr Gale then fled on bike through pathways inaccessible to vehicles.

Using the phone's International Mobile Equipment Identity, investigators found the device had been sold to a woman.

In his recorded police interview played to the court, the complainant told officers that the alleged offending triggered memories of living in a war zone prior to coming to Australia.

"I'm from Sri Lanka, so a lot of things came to my mind at that time [of the alleged offending]," he said.

"I'm from a war zone, all the memories came."

He went to Tuggeranong Police Station shortly after meeting Mr Gale and told officers that he was still shaking "until I came to the police station".

The complainant alleged Mr Gale produced a "shiny, stainless steel" handgun from his hoodie.

He alleged Mr Gale pointed the gun at his legs and held it for about 10 seconds.

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Crown prosecutor David Swan, in his opening, said the case against Mr Gale was that his arranged meeting was "a ruse, constructed so that he could commit the offence of aggravated burglary".

"He had no intention of purchasing the phone, he provided false details," Mr Swan said.

"The Crown says the accused produced a gun - real or imitation - and committed theft of that phone."

He also accused Mr Gale of threatening to shoot the complainant.

Defence lawyer Jonathan Cooper in his opening said the only factor his client disagreed with was the gun allegation.

Mr Cooper said Mr Gale paid for the phone and it was when the complainant counted the money that he realised he had been shortchanged before falsifying a robbery to police.

"The gun is made up. He's not guilty," Mr Cooper said.

The defence lawyer also read an excerpt of a recorded phone conversation between Mr Gale and his partner about shortchanging the complainant.

"I told you if you f-----g shortchanged him, he'd notice it," his partner said.

Mr Gale faces the alternative charge of robbery if the jury is not satisfied the gun's presence is proven beyond reasonable doubt.

Evidence to be presented to the jury includes screenshots of Facebook messages, photos and the complainant's dash cam footage capturing parts of the meeting. The trial continues.

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