Parramatta City 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, providing the sale is conducted wholly within the property boundary.
• Are there any laws controlling the posting of garage sale signs? Temporary signage is permitted only within the property boundary. Posting signs in a public place without consent is an offence.
• Are there limits to how many garage sales one person can hold per year? Not specifically, however Council may consider that frequent garage sales would be a home business/occupation and therefore other controls may apply.
• Are there laws about using the footpath in front of the person's house? The use of any public land requires consent from Council.
• Other comments offered.
• Is there a page on the web site that covers the laws relating to garage sales? No.

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.