Queenstown police were surprised to find cannabis worth about $48,000 in a car in the centre of the town in April.

A Frenchman caught selling $48,000 worth of cannabis to backpackers from a car in central Queenstown was effectively operating a mobile shop, a judge says.

Paul Aubin, 23, was sentenced by the Queenstown District Court to seven months' home detention and 250 hours' community service on Monday after earlier admitting being in possession of cannabis for supply and possession of a bong for cannabis use.

Aubin was jointly charged with Ruben Aboujdid, who is partway through a trial defending the charge.

Aubin had travelled with friends from Christchurch to Motueka to pick up the cannabis, then drove to Queenstown where they tried to sell it to backpackers.

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Judge John Brandts-Giesen said a member of the public called police about 11pm on April 28 after spotting the pair in their car in central Queenstown and noticing the strong smell of cannabis.

Police saw the car near the police station a few hours later and spoke to the men.

They found 2.43 kilograms of cannabis packed into 137 labelled bags and nine small plastic containers. Its estimated street value was $48,000.

Police also found equipment used for consuming cannabis and $960 cash.

Defence counsel Liam Collins told the court the case would be laughable if it was not so serious.

Aubin was "naive and stupid" and the cannabis dealing operation was unsophisticated. Aubin was not a gang member nor a drug kingpin, Collins said.

"He was hoping to subsidise his own cannabis use and perhaps make a bit of money on the side."

Aubin had no previous convictions and had since given evidence against Aboujdid, Collins said.

Judge Brandts-Giesen said even if cannabis laws changed in New Zealand, it was not possible to "go around the country in what is effectively a mobile shop".

He believed Aubin was seeking commercial gain.

"You bought cannabis to sell at a profit. That profit was no doubt going to finance your own addiction but also, I suspect, your holiday in New Zealand."