Attempts have been made to use fake firearms licences to buy guns on Trade Me since two women were fatally shot in Northland.
Quinn Patterson bought firearms on Trade Me and was selling accessories for military weapons until the day he shot dead property manager Wendy Campbell and her daughter Natanya, when they went to carry out repairs at his Whangarei rental on July 26. He later died at the scene.
Police have confirmed that Patterson did not hold a firearms licence.
Trade Me has banned 13 people from the firearms category of the website since the shooting. In the last year, more than 80 Trade Me members were banned from the category.
"In the wake of the incident in Whangarei we had a number of people who were attempting to put either false firearms licences or licences that had been used on other people's memberships into Trade Me to test our systems," Trade Me head of trust and safety, Jon Duffy, said.
"We took that really seriously and we ended up completely terminating one or two [Trade Me] memberships and banning others from the firearms category, just because something really serious had happened and we did not appreciate people trying to test the system."
The Trade Me account used by Patterson was removed from the site after the shooting, however the Herald on Sunday was able to recover data showing Patterson carried out a fire-sale prior to the rampage.
His online trades included selling parts synonymous with sniper rifles and fittings for an AK47.
Police Association president Chris Cahill said it was "pretty scary" that a number of people had attempted to test Trade Me's systems by using fake firearms licences since the shooting.
Trade Me has also revealed it has finally been given access to police records on gun owners to help prevent firearms falling into the wrong hands.
From as early as September, the site will have the ability to query the police firearms database to verify members are using a valid firearms licence and one that matches the details on their Trade Me membership.
Trade Me will require anyone buying, bidding or asking a question on a firearms listing to provide the name and number on their firearms license. Previously, only the firearms licence number was needed.
Discussions about the new procedures had been ongoing for some time prior to the Northland shooting.
Trade Me's rules at the time of tragedy meant those trading - or even bidding or asking a question - on items on its firearms category must first enter a firearms licence number. But there was no facility in place to check that number was legitimate.
"There are a couple of areas where there will be significant improvements in our systems as a result of this access," said Duffy.
"If we reduce the number of potentially dodgy transactions that are happening in the online space, it means there are less transactions going through where people will be trying to circumvent the offline restrictions as well."
Once a firearm has been purchased on Trade Me, the offline part of the process relies on the seller sighting the buyer's firearms licence. If the seller is going to send the firearm, the buyer must have their licence verified at a local police station. Police then send a form to the seller to tell them the buyer is legitimate.
Cahill said it was a real positive that Trade Me had gained access to the police firearms database.
Detective superintendent Tim Anderson, Police national manager criminal investigations, said police commended Trade Me for their "efforts to keep our communities safe".
He said it was a "great initiative" for Trade Me to be able to query information with the police firearms database; adding it would help prevent the misuse of licences which had expired.
"This is a really positive development that will help police's efforts to make New Zealand a safer place to live."
The Police Association and Trade Me want a register of all firearms serial numbers to monitor the flow and movement of guns in New Zealand. Trade Me have also called for more resourcing for police so they can be more active in checking on gun licence holders.
When asked why Trade Me hasn't stopped selling firearms altogether, Duffy said: "If something is completely legal to do, we have to think long and hard whether we want to take the next step and ban the sale of those things.
"Rather than outright banning something, we look to use technology to innovate and make things safer where we can."
Duffy said Trade Me would look at reviewing their systems once a fuller picture of what happened in Northland emerges.