The lead-up to this weekend’s so-called Super Saturday byelections has showcased a practice commonly employed in high-stakes political contests.

In the United States, they call it opposition research. Here, its product has a plainer name – the dirt file.

In the key Queensland electorate of Longman – one of two marginal seats seen as pivotal among the five being contested – the last days of the public battle became extremely willing.

Behind the scenes, it was even worse, including allegations of money being offered in return for damaging testimonials.

In both Longman and the Tasmanian seat of Braddon, most of the dirt has been thrown at third candidates who, barring a dramatic up-the-middle upset, were expected via their preferences to determine which of the major parties would prevail.

In Braddon, the third candidate is local fisherman Craig Garland who is urging his supporters to direct their preferences to the Shooters and Fishers, the Greens and Labor ahead of the Liberals.

After Liberal parliamentarians suggested he was unfit for office, Garland was forced to explain publicly the circumstances of his pleading guilty to an assault charge 24 years ago, after a scuffle with off-duty police officers outside a Geelong pub.

The melee led to an off-duty policewoman – who Garland says grabbed his dreadlocked hair and pulled it – falling and breaking her arm.

Garland says he went to the aid of his friend, who had become involved in an altercation with people who did not identify themselves as police.

“Well, if your friends are under attack, if I saw the same thing here, if I saw two fellas being ganged up with a mob, I wouldn’t stand back and let it happen,” he said.

“I’m not that sort of person. I was brought up different.”

Garland denies vehemently that he hit the policewoman and says he pleaded guilty to a single charge as part of a deal to have eight other charges dropped.

“Last week, I started off Monday, I was ‘Green’. Tuesday I was ‘extreme Green’. Wednesday I was a ‘cop basher’ and Thursday I was a ‘perpetrator of violence against women’. How desperate are they?”

Liberal campaigners promoted the story in the media. Senator Eric Abetz called on Garland to “immediately come clean” about the revelations, published in The Australian.

“It’s interesting,” Garland told Sky News on Wednesday.

“Last week, I started off Monday, I was ‘Green’. Tuesday I was ‘extreme Green’. Wednesday I was a ‘cop basher’ and Thursday I was a ‘perpetrator of violence against women’. How desperate are they?”

In Longman, there was criticism of the LNP’s Trevor Ruthenberg for wrongly claiming he had been awarded a medal for active overseas military service when the medal was a lesser one for service onshore.

Ruthenberg said it was a simple mistake, albeit one that had sat on a parliamentary website uncorrected for years.

But most of the controversy in Longman has swirled around the crucial third candidate, One Nation’s Matthew Stephen, whose how-to-vote card recommends putting the Liberal National Party ahead of Labor.

Opposition Leader Bill Shorten and other campaigners labelled him a “dodgy tradesman” after allegations surfaced that the One Nation candidate failed to pay contractors when he ran a tiling business, Aus Tile Qld Pty Ltd.

Some of the allegations, which Stephen denies, relate to a subcontracted job his company undertook in 2014 at Darwin’s Hilton Hotel.

He says he was left struggling financially when the company holding the job’s main contract refused initially to pay a substantial sum it owed him and that some of his creditors were paid late as a result.

He says adjudication led to the money being paid to him and he – in turn – paid everything that he owed.

But as the Longman campaign peaked this week, two tradesmen gave interviews alleging Stephen still owes them money for subcontracted tiling work they did for him.

Tiling subcontractor Matthew Young told Channel Nine’s Today show that Stephen owes him $6500 and his brother $11,000 for work they did on the hotel renovation job in Darwin. In the interview, Young revealed he had come forward with the pay allegations after the Labor Party contacted him.

Bundaberg tiler Dale Moore told AAP he was owed $4000 and that he had tried for three years from 2014 to get his money.

Stephen denies their allegations, labelling them part of a Labor smear campaign. The Saturday Paper has seen messages Stephen received from two different men this week, alleging they were being offered money to give interviews criticising him.

Stephen says the men, with whom he says he has worked previously, told him a woman contacted each of them and offered $2000 if they would give television interviews criticising the candidate’s business record.

In one case, the Nine Network was mentioned. In the other, the network was Sky News. Both networks deny offering anyone any money for such interviews.

Stephen alleges the men, who declined to speak directly to The Saturday Paper, told Stephen they believed the woman was suggesting she could facilitate interviews with the networks and the offers did not come directly from the networks themselves.

Nine’s news director Darren Wick said his network had made no such offer.

“Nine definitely has not approached [them] nor been approached,” Wick told The Saturday Paper. “Nor would we pay for something like this, ever.”

A spokesperson for Sky News said: “No. There is absolutely no truth to this claim.”

Stephen says both subcontractors told him they declined the offer. He and One Nation reported the incidents to the Queensland Police Service in Caboolture.

“Politics is savage, mate,” one of the men’s messages to Stephen says.

“I wouldn’t do it to ya no matter how much I needed the money cob.”

This week Stephen was also buffeted by allegations relating to the 2016 sale of his tiling business to Irish national Steven O’Donovan.

An undisclosed sum changed hands – Stephen says enough to reflect the assets and liabilities – just two months after the Northern Territory Supreme Court had ordered the now political candidate to pay $13,769.99 to an NT builder, Phillip Hoare, for what the judge described as the tiling company’s poor-quality tiling work on another home-building job in Darwin.

Stephen says he had subcontracted that tiling work to Steven O’Donovan and others because the overall building job was running over time and he had other work he needed to start.

The judge criticised both plaintiff and defendant, each of whom represented himself in the proceedings – rejecting the size of Hoare’s damages claim but ordering Aus Tile Qld Pty Ltd to pay Hoare the value of having the work redone with new tiles.

Two months later, Stephen sold the tiling business to O’Donovan with assets including a truck and tools and liabilities, which included more than half of the damages payout that was still owing.

Hoare says neither O’Donovan nor Stephen ever paid the rest.

It is not clear when O’Donovan left the country to return to Ireland, or why. The Saturday Paper has been unable to contact him. Guardian Australia reported this week “there is no record of Steven O’Donovan or Stephen O’Donovan on the electoral roll or any Australian register of tradespeople”. However, Matthew Stephen claims O’Donovan messaged him on Wednesday night to say he’d been offered “nice coin” for an exclusive interview.

Hoare told The Saturday Paper he has no political motive in pursuing what is owed to him in public this week. He says he contacted One Nation and told the party its candidate owed people money but was rebuffed.

“I’m a Liberal voter,” Hoare says. “I’ve got absolutely nothing against Pauline Hanson. I’ve got no horses in this race. I’m a guy from Darwin.”

For all of the attention it’s been given, the Longman contest is just one of five byelections running today across four states.

While the issues in all five campaigns, which include Perth and Fremantle in Western Australia and Mayo in South Australia, have largely been local, the major parties have also used the byelections to road test national messages they plan to roll out at the full federal election.

In Braddon and Longman, Liberal campaigns have leaned heavily on Shorten’s unpopularity as a key campaign weapon, along with accusations that Labor wants to raise taxes.

Labor has accused the Liberals of putting the welfare of “the big banks” ahead of ordinary people and before providing services, especially in health. It has portrayed Malcolm Turnbull as out of touch with working Australia.

Dirty tricks and dirty laundry aside, the Super Saturday focus has fallen most on the two eastern states’ contests because their results have the greatest political implications.

The Liberals are not running candidates in Perth and Fremantle. In Mayo, former MP Rebekha Sharkie, whose party the Nick Xenophon Team has rebadged itself as the Centre Alliance since Xenophon’s political exit, was the favourite to fend off a Liberal bid to regain a once-safe seat going into this weekend.

Despite the Liberals attempting to capitalise on dynastic sentiment by preselecting Georgina Downer – whose father Alexander and grandfather Alexander snr have both held the seat – Sharkie was set to follow the paths of other independents who have wrested previously safe seats from the major parties and managed to hang on, often for multiple terms.

Victorian MP Cathy McGowan has done it in the previously Liberal seat of Indi as did others before her, including independents Tony Windsor and Rob Oakeshott in their rural New South Wales seats of Lyne and New England, Peter Andren in Calare, Ted Mack in North Sydney and Phil Cleary in former prime minister Bob Hawke’s old Labor seat of Wills.

With Perth, Fremantle and Mayo expected to remain in their incumbent parties’ hands, attention has fallen on Braddon and Longman, both marginal seats Labor desperately needed to retain and the Liberals desperately wanted to win.

The most-quoted statistic of the long campaigns has been that no opposition had lost a byelection in Australia for 98 years. They are seen usually by voters as a chance to give incumbent governments a kick.

The internal party critics of Labor leader Shorten have set the two byelections as a test for his future claim on his position.

Lose two, they say, and he will face a challenge from fellow frontbencher Anthony Albanese. Lose one and it becomes much more complicated. Hold both and Shorten should be safe and deemed to have passed the test, but some are still saying it depends by how much because a narrow victory might not be solid enough to see Labor secure government when the federal election comes.

Those contemplating change risk being labelled as wreckers, shattering years of unity with no guarantee of electoral success.

In the final week of campaigning, Labor has been seeking to reframe the leadership conversation.

Shorten, his parliamentary supporters and even some of his Labor critics have suggested a scenario in which the Liberals fail to win any of the seats – having already forfeited two in WA by declining to contest them – and it is Malcolm Turnbull whose leadership comes under pressure.

Ahead of the vote, the theory was gaining little traction on the Liberal side other than with Turnbull’s publicly declared critics.

“This election isn’t ultimately about me or Malcolm Turnbull,” Bill Shorten said on Wednesday in Longman.

It was, he said, about the locals in these electorates and what they needed.

But the campaigns have also been about discrediting the competition, especially Matthew Stephen, whose One Nation party looked set to secure 18 per cent or more of the primary vote in Longman.

Stephen’s public relations experience is evidence of what’s at stake and of the difference in resources between the big and small parties in vetting candidates, checking histories and having responses ready when the mud flies.

Late this week, there was speculation that despite the troubles with his business past, Stephen’s vote may be largely unaffected by all the negative publicity, with One Nation supporters seeing it as big parties and their supporters going after the little guy.

It appears the absence of his leader Pauline Hanson, away on a European cruise, was unlikely to hurt Stephen’s numbers either.

As for his tiling business, Aus Tile’s current business registration contains irregularities, including still showing Stephen’s home as its registered address and describing O’Donovan as the sole – and non-beneficiary – shareholder, meaning he holds the share for someone else.

Stephen can’t explain either of these anomalies and says he has written to the Australian Securities and Investments Commission this week seeking to query them and have them corrected. But he continues to deny any wrongdoing and says the tactics being employed to peddle information against him, timed for the final days of the campaign, are unfair and will have long-term implications.

“This is really hurting my livelihood,” Stephen says. “If I don’t get elected on Saturday, I’m back on the tools on Monday … Facebook court seems to be the most knowledgeable court in the country. It drives me up the wall.”

But those who maintain Stephen owes them money argue it’s all his own doing in the end.

In the political controversy surrounding Stephen, it’s extremely difficult to tell what’s true and what’s not. And that’s the idea.

The underlying message in these campaign tactics is that while truth matters, the appearance of truth – whether confirmed or not – will suffice.

But the mudslinging hasn’t been one way in Longman.

One Nation produced giant placards of Labor candidate and former MP Susan Lamb who the party accused of hiding from the media. Mimicking a famous movie poster, they depicted a moth on her mouth under the heading “Silence of the Lamb”.

One Nation also engaged rogue former Labor leader Mark Latham – who had actually joined the Liberal Democrats – to record a vitriolic robocall message to voters calling Shorten a liar and saying he shouldn’t be trusted.

Details of the call emerged in the national media on July 9.

Labor registered the dodgytradie.com website the next day.

Stephen is calling it all “political bastardry”.

But few in the game of politics are surprised.

“Everyone looks for dirt on every other candidate,” NSW Liberal senator Jim Molan observed casually on Sydney’s Radio 2GB on Tuesday.

Apparently, all is fair in love, war, business and a byelection with a lot at stake.