Unfortunately, there's a lot of unknown-unknownism going on in that stuff. I've had to watch painfully while people (even "experts") discover things like false-positive rates and PCR cycle count for the first time. It's a bit like living through years of undergraduate science education on fast-forward, but people only read the section headers and never fully grasp the details. Anyone who has actually done a lot of PCR could tell you, for example, that a cycle count in the high-30s is prone to noise, but somehow this became the broad standard we're using in the US.

It's relevant to your comment because a lot of these systems are shoddy (as you would expect), and the confidence in their performance is based more on a faith in shiny things than actual science. So we do things like set up large-scale PCR surveillance, and forget to validate the overall false-positive rate of the system before we start drawing huge extrapolations from the data. Years later, we'll find out that the conclusions were wrong, but nobody will be paying attention by then.

This problem is probably less relevant in NZ than most places. However thanks for the comment (and it’s parent), I didn’t know these things.

Any walk-in clinic is almost certainly going to have a cross-contamination risk, for example.