Relief teaching is different to regular teaching. You are not accountable for the long-term success of your class - that's the poor teacher who regularly takes the class. You DO have a responsibility to the class, the kids, the school and yourself.
You know you won't be around long enough for long-term issues. You won't to be responsible for the NAPLAN results or any other systemic measure applied to measure outcomes. So if you make a botch up job, it won't be your fault, right?
If you botch the job, you may not be asked back to the school and when the word gets around (and believe me, I know principals talk about relief teachers), you may not get much work at all.
So...... work at being the best DARN relief teacher you can!