Stevecro’s points are valid but I think the one on mediation applies to internal mediation processes which are now allowed in NSW. It doesn’t prevent owners seeking mediation through Fair Trading.
Regarding the possibility of NCAT ruling a claim as vexatious, it still requires engagement and a response of some kind, including appearing at the Tribunal (you could respond in writing, but that is risky).
A cleaner but harder to achieve outcome would be to get the owner declared a vexatious litigant by a higher court