NT's family visited the island and stayed in the bach again the next month, when they had a key cut.
The decision says NT knew the owner's brother. They drank together at their local pub. The brother, "Mr K", had inferred he part-owned the bach and told NT he could stay there with his family, giving him a key.
When NT arrived the key did not fit the lock. He noticed the agent's sign and called him to gain entry. NT said he had permission to stay, knew the address and mentioned the complainant's surname.
"Waiheke Island has many non-permanent residents and holiday properties and it is not unusual for people to come and go and to get keys from agents to do so," the decision says.
When the man planned another visit the next month, he phoned the agent who made arrangements for NT to collect the key from his branch office. During the second visit, NT had a key cut, which he gave to the owner's brother.
"When later challenged by NT, Mr K again claimed he was the co-owner of the property and/or that it had been put in his sister's name because of financial issues he faced."
The owner visited her bach in January 2014 and found personal items belonging to NT and his family and confronted the agent. The locks were changed.
Three weeks later NT and his family wanted to holiday at the bach but found the key cut did not fit the lock. They contacted the agent who told them to contact the owner.
"NT did so and learned the truth about the ownership of the property and that no permission had been given for him and his family to use it. NT was adamant that this was the first they knew that they did not have permission to use the property."
The owner later demanded compensation of $146,000 from the agent, then lodged complaints against the agent.
The decision also faulted the agent for dropping the asking price by $100,000 without the owner's written permission, a lack of correspondence about the marketing process, and failure to adequately disclose the commission.
Other complaints relating to alleged defamation, compromising the property's security and "degrading and humiliating" behaviour were not upheld. The committee is yet to issue its decision on orders or penalties.
The agency which employed the agent said it would review the decision.