Buy a $20k car? Tax rate is 20%. Buy a $100k car? Tax rate is 50%. Buy no car? Keep your money.

Uncle Sam doesn't need, and shouldn't be able, to know how much money I have.

It could get very complex to identify and enforce a variable sales tax rate, but we've already got enormous armies of govt workers so that's nothing new.

It would be harder to cheat, and you'd be in control of how much taxes you pay because if you go luxury you're gonna pay more.

No ongoing tax on property either. Just the initial purchase and then of course any upgrades or whatever, you pay taxes when you buy.

There, no more tax filing for individuals. Business tax filing would be so much simpler as well. Oh, you sold X of item 1 so that's $$. You sold Y of item 2, that's $$$$.

What am I missing that this isn't a good idea?