Both companies sell properties in some of Auckland's most desirable suburbs, but in an email sent to NZME. News Service when charges were laid, Tucker said the bad blood was "not about turf".
"It's about ethics, integrity and honesty," he said.
Judge Ryan said there was a complex context to the incident, which had seen him leave the company after successfully taking a dispute to the Real Estate Agents Authority.
Also in the background was the breakdown of his relationship with his then partner.
The judge said she had attacked him with pepper spray, for which she appeared before the court.
In February 2014, he received a package containing a glass jar full of faeces from an unknown sender.
Tucker assumed it was from his former employer, from whom he had received correspondence shortly beforehand.
The court heard how he glad-wrapped and bubble-wrapped the jar and sent it back to where he believed it had come from.
On its way there, the glass smashed and the stinky contents "seeped out".
Wills' lawyer David Beard said his office received a package in a courier bag along with a letter bearing Tucker's company letterhead.
"It was opened on the steps of the Auckland Central Police Station with myself and a constable and ... I was gagging over the side, with tears in my eyes," Mr Beard said.
"I'd just been to the High Court that morning, so I was all dressed up in the black suit, the works, with haz-mat gloves."
Posting a noxious substance attracts a maximum penalty of a $5000 fine but Mr Beard believed it was a more serious offence.
"What's the difference between sending that and a package of smallpox? It's noxious, it hurts people, it's full of bacteria, it's harmful," the lawyer said.
"In 16 years I've never seen anything like this in my career, and I have to deal with some interesting people."
Tucker's lawyer Ron Mansfield said the lawyer might have been more "robust".
It is understood police did not have the contents of the package analysed because of health-and-safety concerns and it was subsequently destroyed.
In considering his application for a discharge without conviction, Judge Ryan outlined the defendants various health issues.
He had a heart defect, a metal plate and screws in his ankle and elements of bi-polar to his character.
"I have no idea whether that affected your decision making when confronted with a container of faeces," the judge said.
She was satisfied, however, that the low-to-moderate-level offending was outweighed by the impact a conviction might have.
Tucker will now have to go before the Real Estate Agents Disciplinary Tribunal.
