The by-election campaign for the federal seat of Mayo has been “very dirty” but nothing less than she expected, Centre Alliance candidate Rebekha Sharkie claims.

Ms Sharkie took particular aim at posters around the electorate featuring her next to Opposition Leader Bill Shorten, and also a media report on her personal life.

“But I am refusing to buy into it. I knew it was coming,” she told ABC radio Wednesday.

Her comments came amid an on-air debate with Liberal candidate Georgina Downer, who said her campaign had also been tough, with her social media accounts trolled among other issues.

“But I did grow up in politics,” she said.

With just three days to the Mayo vote, pre-poll centres across the sprawling Adelaide Hills electorate remain the focus of attention, with both candidates hitting the streets to drum up for support.

Ms Sharkie has waged her campaign with limited resources, but has been backed by federal independents including Bob Katter and Andrew Wilkie.

Meanwhile, a string of Liberal Party heavyweights have come to Adelaide to offer their endorsement for Ms Downer.

Ms Downer (L) said her social media accounts were trolled. Photo: Facebook

Prime Minister Malcolm Turnbull has visited twice, as well as former prime minister John Howard and senior Liberals Julie Bishop, Greg Hunt, Michaelia Cash, Simon Birmingham and Nationals Leader Michael McCormack.

Ms Sharkie welcomed the high level of attention the seat is receiving from the federal coalition.

“I particularly like it when they bring a cheque book with them,” she told AAP.

“Make no mistake, if I wasn’t running they wouldn’t be here and they wouldn’t be making promises to our community.” 

Ms Sharkie won Mayo at the last federal election, but was forced to resign earlier this year after being caught up in the dual-citizenship saga.

Ms Downer is seeking to follow in her father’s footsteps. Former foreign minister Alexander Downer held the seat for more than 20 years.