When you sell your car to someone, there will be a transfer of ownership to you and this will leave a paper trail for the IRS or whatever tax authority. When they audit you or if someone else report you to the tax authorities, you will have to explain your wealth to them and what you used to pay for that.
Governments and tax authorities have full control, no matter what you think.
I agree. Even in the cryptocurrency world, governments still can implement taxes through our local exchanges and that is why we are paying it passively everytime we convert our cryptocurrency funds into fiat money. Being in a cashless society will still be under controlled by governments and we cannot escape or evade tax generally. Bitcoin will be our best investment or other cryptos while fiat will be good for economic stability so I think having both assets will make sense.Governments and tax authorities have full control, no matter what you think.