thanks Tracey,
I contacted both the ATO and my accountant and got the feeling that the ATO support while friendly and curious,
was not fully sure, seemed to indicate that the person never really got hired, so STP would not apply. I still had to run this as wages but with a payment summary. All this was fairly unclear to me.
My accountant was sure that payments made to individuals for their time spent in an assessment or interview process, even if they do not end up taking the job, are still considered taxable income in Australia and are subject to Pay As You Go (PAYG) withholding.
As the “employer” (even though you did not become one), you would also be required to withhold tax from the payment and report it to the ATO through the STP. If they do not provide Tax File Number the withholding rate is 47%.
Regarding Superannuation, if the individual is considered an employee for tax purposes, the employer would be required to make superannuation contributions on their behalf, even if the individual does not end up taking the job.
So, that's what I did in this case - lot's of work for a dud interviewee but I am still glad we discovered this problem early and don't have to deal with him later on.