CSA needs to look at individual cases... I think that the government has a rough figure on how much it costs to raise a child: say if it is $5000 a year, then each parent should pay $2500 each...
This should be done in mediation and reviewed in a suitable amount of time if the Paying parent pays $70 per week the receiving parent should have to produce a certain value but not the whole value where that has been spent on the child especially in extreme circumstances.
Mediation is usually done when parents want access of the child so the amount of child support should be discussed within that.. and it should not change just because you have earned $50 more. The cost to raise the child did not go up just because the paying parent done an hours overtime. And for unexpected situations (medical, dental) half it when it happens. Paying parents should not be punished for earning an income, you will find a lot more parents declaring their incomes properly if it were a lot fairer.
If a paying parent believes that the money is being used for things other than supporting the child/ren there should be another aspect where they can use the funds for schooling events ( my stepson never went to one school camp, never attended one school excursion, never had any school photos, never went to his year 12 formal, for the first 1/2 year of high school never had uniform he was wearing primary school uniform etc) and we were paying $200 a week toward the end.. started at $85 about 8 years ago and just kept going up then as I mentioned on other post day after 18th b'day was booted out of home cause child support stopped..
I am sorry if I offend anyone with this post!