In a subsequent property inspection, two separate neighbours told the owner they thought a brothel was operating from the unit because cars were calling late at night and two women were "meeting and greeting various men".
"[The owner] also says he was told a plastic flower was put out in the garden to indicate the premises were open for business," the tribunal adjudicator said.
Meth testing then found the unit had been significantly contaminated and when the owner contacted Tenancy Services' advisory team, they said the rental was probably uninhabitable.
The owner and Fitzgerald subsequently agreed to end the tenancy.
Fitzgerald was then seen by neighbours doing "excessive cleaning" at the premises and washing down the walls with sugar soap.
Forbes and Fitzgerald, for their part, denied running an unlicensed brothel.
Fitzgerald said he had a foreign language student and her relative stay at the unit and "both had lots of visitors in and out of the premises".
Forbes added that her work with the New Zealand Prostitutes' Collective supported "the health and safety of sex workers, but she denies any involvement with the two women who were staying at the premises".
To explain how the unit became contaminated, Fitzgerald said another boarder had also stayed. This person worked for a company that "carried out decontamination of meth houses and he may have carried traces onto the premises".
Fitzgerald produced no evidence to back the claim, however.
He also presented drug-screening tests for three months in 2017, showing he had no methamphetamine in his system.
But the adjudicator found the tests inconclusive because they only covered a short period of the tenancy and didn't rule out the use of meth at other times.
The tests also showed Fitzgerald had used methadone and cannabis.
The adjudicator subsequently said the meth-testing results, neighbours' observations, Fitzgerald's use of other drugs and his installation of a security camera led him to believe meth had been unlawfully used at the rental.
"Taken together, the weight of evidence is sufficient to enable me to draw the inference, on balance, that the tenants have used, or permitted the premises to be used for an unlawful purpose," the adjudicator said.
He ordered Forbes and Fitzgerald to pay the owners $450 for unlawful use of the rental, almost $3000 to cover the cost of meth testing and $420 in unpaid rent.