As part of your property research it's important to not only keep track of suburbs where prices have increased but also suburbs where prices have declined.
The following article by Elizabeth Redman from Sydney Morning Herald demonstrates this by listing out the top 20 suburbs in Sydney where unit prices have declined in the last 5 years - https://www.smh.com.au/property/news/the-sydney-suburbs-where-property-prices-have-lost-ground-over-five-years-20230927-p5e84q.html.
See below three of these suburbs (Rushcutters Bay, Chippendale, and Harris Park) using PropertyDirector's Suburb Capital Growth Report where unit prices have declined in the last 5 years due to new apartment developments oustripping buyer demand over this period.