The co-offender then ran down the road where Britton, who had followed the pair, picked him up.
Defence lawyer Wiremu Puriri argued Britton had not been involved in planning the robbery, was not party to the airgun being procured and was not privy to the details of the robbery.
"He was told to position himself at a certain point and to follow a certain vehicle when it went past," Mr Puriri said. "His plea was an acknowledgment of his involvement."
Mr Puriri said Britton, of Dargaville, was remorseful, had written three letters to the court indicating his remorse and had attempted restorative justice with the salesman.
Britton and his whanau had already paid $3500 as recognition of reparation and he had voluntarily undertaken drug and alcohol counselling.
Crown prosecutor David Stevens accepted Britton had played a lesser role in the offending, but said it was clear from texts between the two offenders the aggravated robbery had been premeditated, and Britton was aware of the airgun which had been purchased from a third party.
Judge Davis said he was prepared to accept Britton may not have known all the details in that he may not have known who the victim was, but he had known it was an aggravated robbery, had agreed to drive the getaway car and had also agreed a "faster vehicle" would be used.
"You knew a serious offence was to take place. Your involvement may have been less, but it was still significant," the judge told Britton.
"Prison is the appropriate outcome," Judge Davis said.
In sentencing, from a starting point of 46 months, he allowed a discount of six months for Britton's remorse and the steps taken to address the issues as well as a 25 per cent reduction for an early guilty plea. The 30-month sentence is subject to parole conditions.
He also directed a three-strike warning be given.
The judge thanked Britton whanau present in the court for their support and letters.
"I have been moved by them and you have had a significant impact on the reduction of the sentence," he said.
