The Australian implementation had a lot of problems. Instead of being (something reasonably loophole free like) a tax levied on fossil fuel consumption it was a scheme that applied to the 500 largest emitters. These emitters then (crucially) estimated their own emissions minus offsets and paid tax on that.

The issue with this is that it creates a whole parallel (and largely fake) carbon accounting world. Fake estimates, fake offsets, a complex web of compensating subsidies - but real public money.

The field of carbon taxes is tricky because we can imagine simple schemes which handle a few scenarios in a fair way (ok, fuel! we know how to tax that) but once you start thinking about agriculture or construction you quickly get into complex estimation. You then end up with armies of carbon accountants who spend all day looking for loopholes and rorts.