There is no indication of Captain Biffs D17S aircraft registration on his website, but I would presume he's wearing U.S. registration? The one pictured for sale is perhaps VH-FNS?
Aircraft Hire - Cessna, Piper, Beechcraft, de Havilland and more - Sydney, Australia
EDIT - Ooops, my error - the registration is there, I missed it, it's N16S ....
Aircraft N16S Photo by GeeDee9
It seemed a little at odds to have his plane for sale, at the same time as he has great plans for a round-the-world jaunt.