I feel that you have gone from facilitating tax evasion via a “marketplace” on this forum to a general marketplace.
Yes a marketplace buying/selling goods clearly places the issue in the hands of buyer/seller, unless the site owner has provided the site for that purpose.
But providing a place for people to work and evade paying tax comes under very different laws. In the USA the constitution provides a separation as long as the purpose of the site is not for that. In other countries there is not such protections.
Tax evading laws are very powerful and even giving loose advise in Australia on how to evade tax is an offence. Thus facilitating/managing it as the site owner and/or moderating falls under that law.
Now as to whether that law would be used to go after moderators living in Australia, I do not know, but it is available to them.
AND as I said above I do not wish to test that law (in court)
AND no it is not overthinking it. Its just trying to answer your questions that make it so.