Collectors in Newcastle and the Hunter Valley region can take their stamps to the monthly Stamp and Coin Fair for valuation. This event is held in the Wallsend Pioneer Hall on the third Sunday of each month, from 10am to 4pm. Local coin and stamp dealers are in attendance, who will be able to tell you about your collection. They may offer an opinion as to the value or otherwise.
Alternatively, you can contact a stamp or coin dealer direct – you will find a list on the Stamp and Coin Dealers of Australasia website. Click on this link: www.scdaa.com.au/members/, or the Australian Philatelic Traders Association website, www.apta.com.au/
Note that not all dealers are members. A part time dealer may live near you.
The Australian Philatelic Federation have an excellent website, which includes advice on how to sell a stamp collection you have inherited. Click on this link: https://apf.org.au/selling-valuing-stamps/