Penrith 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? Residents are not required to have a permit to conduct garage sales from within their property boundary.
• Are there any laws controlling the posting of garage sale signs? Recently council agreed for residents to display garage signs within their local area, however, these signs are to be removed at the completion of the garage sale or risk enforcement action from Council Rangers. Signs are not to be displayed on chevrons at roundabouts or over other safety signs.
• Are there limits to how many garage sales one person can hold per year? Not aware of any restrictions to the number of garage sales that can be held each year; however, should these sales become unreasonable, council may request you to justify the validity of your business.
• Are there laws about using the footpath in front of the person's house? The footpath or nature strip areas from the property boundary to the kerbing of the gutter is a road related area i.e. public land. Council does not support the use of public land for garage sales.  All goods and chattels must be kept wholly on the property owners land.
• Other comments offered.
• Is there a page on the web site that covers the laws realting 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.