The action followed a ruling by The Real Estate Agents Disciplinary Tribunal that Rankin should have told the family about the report carried out by a previous buyer which showed it was contaminated with P.
The family's own tests confirmed the levels of P found in the house was above the ministry's safe guidelines and the Brogden's daughter and her pre-school children moved out while the house was cleaned up.
The family then complained to the Real Estate Agents Disciplinary Tribunal.
Rankin was suspended for three months, found guilty of two charges of misconduct and fined $3000.
Auckland-based lawyer Adina Thorn, who worked with Key to obtain a settlement for the Brogdens, said the REAA's findings showed it had been a really hard experience for them.
It was great that couple had closure and was pleased to have been part of the solution, she said.
Key told the Herald last year that his clients and never wanted publicity about the case.
At the end of last month the Prime Minister's chief science adviser Professor Sir Peter Gluckman released a report which found there was no evidence third-hand exposure to methamphetamine smoking residue on household surfaces caused adverse health effects.
The findings have raised uncertainty for homeowners and agents who have to follow the existing rules until they are changed.