I don't know why Deck Man has been called to the inquest (he's named by
News.com.au, 18 July 2019). Someone with the same name (GO) regularly advertised in Kendall's community newspaper as a provider of services including electrical, plumbing, carpentry, cleaning, lawn mowing, and so on. See page 10 of
The Kendall Chronicle, 05 Sep 2014 (a PDF).
According to Reverse Australia Directory, the address for the landline number shown in the advertisement was residential land in Logans Crossing, last found June 2015.
I haven't seen any reason to suppose any of this is related to William's disappearance. Maybe the Coroner has questions about the house or property maintenance?