These sorts of things are accounted for when calculating child support obligations, and in any case judges are not computers and can use their discretion in such matters. As long as you're operating in good faith you shouldn't have any issues. I was specifically referring to incidents where someone is wilfully disobeying the child support order, such as by quitting their job to work for cash 'under the table' so they don't have any official income to garnish.

>Is it really fair that previously they got to work hard to buy their kid nice things, but now they must work hard to buy them nice things or go to jail?

It's not about buying nice things, it's about making sure the child is not disadvantaged by the separation of the parents. That means keeping the same standard of food availability, clothing, access to education, and so on.

Think of the reverse perspective - is it fair for a child to have to, for example, give up after school sports, because one of their parents decided that they would prefer not to pay child support? Or be forced to change schools and lose their social group because tuition is unaffordable on a single income?

The welfare of the child is often best served by allocating custody such that a child can stay at one residence most of the time (with regular visitation to the other parent to maintain the relationship), so that the stability of the child's living situation is not disturbed by having to constantly switch between two residences, having their school routine and social life disrupted, etc.

Also, custody split is only part of the issue. Supposing parent A earns 2x parent B's income, they should still be paying child support even if custody is 50:50, so that the same standard is maintained across both households.