The complainants said they offered to pay $2500 commission, but the licensee said JVL Prestige director John Van Lienen would not accept that amount.
A deposit by the buyers was paid, but because there was a dispute over commission, $15,000 was held in trust.
In March last year, the complainant's lawyer offered a final commission amount of $8000 and if that was not accepted, they would make a complaint with the authority, the report said.
The agency's lawyer said he welcomed the dispute being adjudicated by the authority and they were withdrawing their offer of $15,000 commission.
The authority ruled the agency had no authority to withhold part of the complainants' deposit.
It censured Mr Van Linen and fined him $1500. The agency was also censured and ordered to pay $4723 in fines and costs.
Meanwhile, another real estate agency has been censured and fined for newspaper advertisements that stated other agencies were profiteering when charging out advertising.
The advert by Tall Poppy Real Estate read: "You won't catch us profiteering on advertising. Tall Poppy is possibly the only NZ- wide agency that doesn't profiteer when charging out advertising. We're told that other agencies add a hefty margin and pocket the gain."
Christopher Packer from Kapiti Properties said the advert was untrue, misleading and brought the industry into disrepute.
The agency told the authority it was a matter of some companies taking advantage of clients' ignorance and quietly taking unearned profit.
It said there was anecdotal evidence that most agencies added a margin to the cost price of advertising to arrive at a retail price.
However the authority said Tall Poppies provided no evidence of its claims and the advert brought the industry into disrepute.
It censured the agency and ordered it to pay a $2000 fine.