Brenton, probably a good option for dad to fly down and inspect. However if he is comfortable and don't mind a drive considering he may need to any way if he buys, then a trip to Vic whilst being prepare is an option. We had a similar issue when buying our van.
We agreed to purchase our expanda sight unseen from a private seller in Vic when we lived in NSW Blue Mts.
We agreed with sellar on the price and sale being conditional on the van being in the condition as described. No deposit was asked for but a commitment from both parties on our intentions. We pre arranged a few things before leaving including a security check on the van, the funds being sufficiently allocated to a few accounts so we could do an online payment from each account within withdrawal daily limits at pickup if satisfied.
We then drove down to Vic ready to buy if satisfied. It worked out for us, van as good as described, owner genuine. If it wasn't what we expected the owner knew that we would not purchase and we would have had an enjoyable drive any way.
The only thing we forgot was arranging insurance but fixed that around 5 km down the road after towing van away via a phone call.The other thing clarifying the tow plug socket type, but a quick trip to super cheap after viewing van fixed that problem.
Good luck to dad.