Actually, it depends on the agent and the seller.

Advertising can show the same listed price until the property contract is finalaized. Then the agent may decide to change the listed price and disclose the real sale price... or opt not to disclose it at all!

Calling the agent's the best way to find out what price the property achieved.

I use onthehouse.com.au to search sale prices of a house but that's only after they've been through stamp duty registration with council and that can take months from date of sale. Still, it's a great site for research and to check out what the market is doing.