Malcolm Turnbull made a "mistake" by failing to stand shoulder-to-shoulder with Coalition candidates at a number of press conferences in marginal seats, Tony Abbott's former chief of staff Peta Credlin says.

Key points: Credlin criticises Turnbull for failing to stand alongside candidates

Credlin criticises Turnbull for failing to stand alongside candidates Mr Turnbull addressed "politics in the pub" in Darwin

Mr Turnbull addressed "politics in the pub" in Darwin Head to Australia Votes for more election coverage

Ms Credlin, who helped engineer the former prime minister's victory at the last election, said Mr Turnbull had not invited candidates to accompany him for his formal press conferences in three electorates so far during the campaign.

"When it becomes a pattern, the pattern becomes a problem," she told Sky News during her regular slot as a commentator.

Mr Turnbull did not appear alongside Sherry Sufi — the controversial Liberal candidate for the Western Australian seat of Fremantle — on Monday.

When the Prime Minister was pressed about the conspicuous absence, he said he expected Mr Sufi was out "doorknocking".

He went on to confirm he disagreed with Mr Sufi's opposition to same-sex marriage and Indigenous recognition in the Constitution.

Ms Credlin said "once in a while a candidate not being at a press conference in an electorate is fair enough".

She said candidates were not present for the media conferences in the Victorian seat of Dunkley and the South Australian seat of Boothby.

The candidates attended the media events but were not standing with the Prime Minister in the nationally televised press conferences.

Describing that move as a "mistake", Ms Credlin added: "They're seats we must hold."

"We've got retiring 20-year members going and anything you can do to boost name recognition [for the new candidates] is important."

Candidates in both seats did campaign alongside the Prime Minister during his visits, but he faced reporters solo.

Ms Credlin has previously described the Prime Minister as "Mr Harbourside Mansion" and her former boss Mr Abbott has described her media appearances as "riveting viewing".

Her latest comments came as Mr Turnbull faced a willing audience at a "politics in the pub" event in Darwin alongside coalition backbencher Natasha Griggs, who holds the marginal seat of Solomon for the Government.

She defused a potentially damaging question from the floor about the fate of $300 million announcement in December to help fight ice addiction, which Mr Turnbull was unable to answer.

In another question, a local renter told Mr Turnbull he would welcome a fall in house prices under Labor's proposed negative gearing wind-back.

"Being able to afford a house is quite appealing to me," he said.

Mr Turnbull said the proposal was all about raising tax.

"This is a dangerous move by Labor, it's not going to improve housing affordability," he said.

Editor's note May 17, 2016: When it was originally published this story asserted that Peta Credlin said candidates in Boothby and Dunkley did not campaign alongside the Prime Minister during his visits to their seats. The ABC accepts this was incorrect and Ms Credlin was specifically referring to their failure to appear alongside Malcolm Turnbull at the formal press conferences with reporters.