There are a lot of variables that impact your listing placement, so it's difficult for us to give you an exact answer. Usually, when a listing is further down the page, it indicates that the ones above your own have purchased Realestate.com.au upgrades.
Upgrades are an additional paid service provided by Realestate.com.au to help agents control listing placement. Upgraded listings will always display first i.e. Premieres, Highlights, Features, followed by standard listings. All listings are also ordered newest to oldest. As your listing ages, it will continue to move down in search results as new listings come onto the website.
If you'd like a quote on an upgrade, you can find this and more information when logged into your account on the left-hand side under 'Realestate.com.au Upgrades.' - Please speak to our staff before making a purchase, as sometimes these just aren't beneficial. :)