Joshua Calthorpe has a long history of ripping people off, mostly on Trade Me. But it was his switch to violent offending that alarmed a judge yesterday, and earned him almost six years behind bars.

The 35-year-old was yesterday sentenced by Judge Mary Beth Sharp in the Auckland District Court to five years and eight months jail - at least half of which he must spend behind bars. He had admitted three charges of obtaining by deception, one of blackmail and had been found guilty of aggravated robbery, after he held a knife against a 25-year-old tourist and threatened to stab her.

He received five years and eight months' jail for the aggravated robbery and blackmail, to be served concurrently, and 18 months' jail for each obtaining by deception conviction, also to be served concurrently.

Crown prosecutor Henry Steele said there had been an alarming escalation in the nature and type of offending by Calthorpe and a significant jail sentence was appropriate.


On the obtaining by deception charges, Mr Steele also said Trade Me had described Calthorpe as the most prolific offender in their 16-year history.

Defence counsel Jonathan Hudson said Calthorpe was remorseful for his offending, and had entered an early guilty plea to the blackmail charge.

The aggravated robbery was a significant incident of violence, but Calthorpe had not previously been convicted of violent offending, Mr Hudson said.

The incident occurred when a 25-year-old Chinese woman visiting New Zealand agreed to meet Calthorpe on an Auckland roadside to buy an iPhone 6. Calthorpe got into the woman's car at her invitation because it was raining and after offering an excuse as to why he did not yet have the phone, the court heard.

When the woman tried to leave about half an hour later he pulled a knife and pushed it against her, demanding her handbag. She later told police she could feel the blade.

She initially refused to give him her handbag, prompting Calhouse to say he would stab her. The woman eventually gave him $1500 but was so traumatised she crashed into another car when she eventually drove away.

The Trade Me fraud occurred when Calthorpe set up bogus seller accounts and sold unsuspecting buyers cars that did not exist. The three victims lost a total of $10,965, with the worst affected out of pocket by just under $5000.

None of Calthorpe's victims had received their money back, and he did not have the means to repay them, Judge Sharp said.

Trade Me head of trust and safety John Duffy said they were pleased with the sentence.

"We take this very seriously and work hard with police to help them prosecute offenders. We learn from every incident and we're constantly reviewing security measures to ensure we keep ahead of the fraudsters."

The blackmail took place when Calthorpe was behind bars. He recruited a child to text the partner of a former cellmate, threatening harm to the former cellmate, his children and grandchildren unless $70,000 cash was handed over before the end of the day.

The woman went to police, who busted the scheme after intercepting texts.

Whether the threats of harm would have occurred was another matter, Judge Sharp said.

"But the level of threat inherent in this behaviour and the duplicity and planning are quite extraordinary."

It was clear from Calthorpe's history that he was a prolific fraudster -- he had amassed all of his 70 convictions since 2010 and 61 of them were fraud related, she said.

But the escalation of his offending to acts of violence was "extremely worrying".

"He's graduated from near fraud or trickster activities to an aggravated robbery where a knife was used ... I consider the offender is dangerous to the community, I'm sorry to say."

She accepted his offending may have been drug-related, and he had also written a nice letter to her, Judge Sharp said.

"I only hope he is not trying to scam me as he scammed so many others."