Evading small amounts of taxes are an example of black market activity that most societies tolerate at a low level because otherwise the transaction costs are too high and stifle economic activity.
For example, it might be a good for society for someone to help,out in their neighborhood doing small jobs. If it’s not a lot of money, the tax implications are low, but trying to enforce taxes on someone who made $100 by helping a neighbor will not only cost more than the taxes reclaimed, but the knowledge of strict enforcement may deter people from doing odd jobs that need to be done.
The Soviet Union tolerated a huge black market and looked the other way as people got rich off it, because the black market was needed to help fix the horrible inefficiency of state planning and distribution of goods. Something similar goes on at the very low end of tax compliance.
If we get scrutinized by tax agencies hard enough that you can’t hide even a small bit of a cash transaction, it will have a chilling effect on small ad-hoc jobs, the ability of illegal immigrants to work, small business startups (which often start as a small ad-hoc cash business then become legit as they grow), and other useful activities we’d like to see people keep doing.
But for that to work, it can’t get out of hand so governments will not admit that they will accept a low level of avoidance, there have to be constant audit threats, etc. Occasionally someone at the high end of what’s tolerable must be publically charged and punished.
But if a government actually decides to drive tax evasion to zero by micro-managing small transactions, it will damage the economy.
Take the eBay thing. If you are buying goods and selling them on eBay as a business, by all means you should pay taxes. But if you are an individual liquidating a few things you own, you shouldn’t. And we want to encourqge as much of that kind of activity as we can, as it moves goods from low-value uses to higher-value uses. It’s like making new things people want, without using any new materials.
But if I have to worry about claiming the sale of my old stereo on my taxes, or I know selling it on eBay could trigger an audit that will require me to hire an accountant and spend hours doing paperwork, I’ll leave the damned stereo in the basement and no one will extract any more value from it. That’s a bad outcome.