Any sale of a rego'd bike will give the seller's details to the buyer.
Similarly, if I was buying a bike in these circumstances, I would want to see the seller's licence, etc before sending thousands of dollars into the wild blue yonder.
So... It would pay to be very careful, but - based on what's been said - I'm not convinced that it's a scam.
Phone calls (not texts) from phone numbers that aren't blocked, are a good start to proving theyre a non-scammer, but definitely not the be-all and end all. See if they answer calls from blocked numbers.
Maybe explain why you(r mate) is cagey about handing out all of the details, and pay careful attention to how he answers. Maybe a worthwhile deposit and let the cheque clear, before sending the details?
There was a scam involving international money transfers that could be reversed even after they'd apparently cleared into someone's account. I am unaware of anything similar with Aussie cheques, but anything is possible...