Pittwater Council has kindly offered the following comments (in blue) relating to garage sales.
 
(If there is no blue answer on a particular question, then a comment wasn't made.)
 

• Are permits required? No.
• Are there any laws controlling the posting of garage sale signs? Advertising signs can not be placed on public land or affixed to public property but in general Council would not seek to remove signs and would anticipate community responsibility and cooperation in removing the signs immediately after the sale has taken place.
• Are there limits to how many garage sales one person can hold per year? There is no limit to the number one person can hold each year providing it is genuine in its nature and does not progress to a commercial activity.
• Are there laws about using the footpath in front of the person's house? The road reserve in front of a private property may not be obstructed by the display of goods for a garage sale.
• Other comments offered.
• Is there a page on the web site that covers the laws relating to garage sales?

Disclaimer:
1) Laws are always subject to change.
2) If there is any doubt, you need to confirm current council laws.
3) egaragesales.com.au provides this information in good faith, but will not be held liable or responsible for any losses or penalties incurred as a result of changes to, or misinterpretation of, current council laws as amended from time to time.