"I can assure you and I can assure Nicky Hager that that's never ceased," Slater said. "I'm effective because I have a vast network of people - including the media - that I talk to across the political spectrum, behind the scenes. That was left out of the book."
The case - in which health academics Douglas Sellman, Boyd Swinburn and Shane Bradbrook have sued for defamation - arises from a series of blog posts between 2009 and last year, and was prompted by revelations in Dirty Politics, published in 2014.
The book was based in part on Slater's emails provided by the hacker Rawshark, and centred on his relationship with central National Party figures including John Key and Judith Collins.
Slater, the former author of the WhaleOil blog, is accused of being paid to write the posts by ex-National MP Katherine Rich through her employer the Food and Grocery Council (NZFGC).
They accuse Carrick Graham, son of the former National cabinet minister Sir Douglas Graham, of being the middle man.
The defendants have tried to get the case struck out - including on the basis that Slater is bankrupt - but the court has declined.
Today's hearing was an oral examination of Slater and Graham before Justice Matthew Palmer after the pair gave previously "inconsistent" written answers during the case's discovery phase.
Slater was unrepresented. His previous lawyer, Brian Henry, was in the court but said he was no longer appearing as he suffered from shingles.
"I'm here as a friend," he said. Henry told the court that due to a stroke, Slater would only be able to take questioning for an hour before he began to struggle.
Slater limped as he walked to the witness stand.
Lawyer Davey Salmon spent the hour trying to ascertain who wrote the blog posts about the academics, and who paid for them.
Slater said repeatedly that he was not paid for blog posts, but for his services in PR, marketing and strategy.
Salmon asked why Slater chose to write about the specific topics covered by the court case.
"It was broadly in line with our own political beliefs that people who receive public moneys - in our vernacular we called them troughers - should be accountable for it," Slater said.
He talked about how the academics received money for research, and were "constantly" in the media framing the political debate - such as the need for a sugar tax.
"My position is if someone's going to advance a particular argument about taxation then I'm entitled to … take a position that opposes such a tax," Slater said.
Salmon then asked what motivated Graham.
Slater said it was the same as him: "Sometimes it's political, sometimes it's for a laugh. That's what I do, I'm a provocateur," he said.
Salmon said that Graham was paying him to write the posts.
Slater again rejected that, saying he wasn't paid for blog posts or their content.
"What I put on my website is my opinions and no one can buy those opinions," he said. "No one pays me for blog posts, contrary to the fantasies of Mr Hager, that's never happened."
When Salmon cited a $900 blogger fee for writing about a teacher who beat his wife amid the documents, Slater again said he wasn't paid specifically for the posts, but for advice.
"The only thing I could say was that it for was PR advice or strategies around making sure a particular person was getting media attention," he said.
Later in the hour, Salmon asked about whether Slater ever received direct payments from Graham's clients, including the Food and Grocery Council, or companies with an interest in sugar, salt, alcohol or tobacco.
Slater said he didn't think so, other than two invoice lines from the council.
Salmon also asked why, if there had been so much communication between the two - including admissions from Graham that he wrote draft blog posts for Slater - those documents were not included in the discovery documents.
"I have no idea," Slater said. "If I had them I'd have given them to you."
When Salmon pushed him, Slater snapped back.
"Why don't you ask your hacker friend? I was hacked by a criminal. A vast amount of damage was done by a criminal hacker and now you're saying that's my fault?"
About three-quarters of the way through questions, Henry told the court that he could see Slater was struggling and the judge urged Salmon to wrap up.
After revealing he no longer had access to the back-end of his website because it had been ceased by liquidators, Slater was excused from the stand.
Graham will undergo examination this afternoon.
