alt Hacker NewsReal estate is a bad example because it's already subject to property taxes, which is a form of wealth tax. Maybe it doesn't need another wealth tax.
Private businesses are a better example. They don't trade on markets, sometimes don't have multiple shareholders. There already exist methods for valuing businesses (discounted cashflow, for example). Let the taxpayer pick one and make them stick to it.
> You could pay for these using the 30% of the assets that have some practical degree of liquidity
I already said "no liquidations, pay with assets". For non-liquid assets pay with IOUs on said assets. The government cashes in the IOU when the asset changes hands - whether it's by sale, gift, or inheritance. Yes that's an inheritance tax; who cares? If you want to add a wealth tax to real estate, this is the way to do it.
There are a surprising number of edge cases out there.
Quite a few assets can never clear a market — they have value in some abstract sense but no concrete sense. For example, assets that are legal to own and transfer but illegal to buy or sell.
Some commodity assets have value that it is nonetheless not always transferrable. A common example relevant to wealth taxes is intangible assets where value is bound in who owns it and not the asset per se. Most of the value vanishes the instant you transfer to e.g. the government.
Another common issue is that wealth taxes can directly conflict with existing load-bearing contracts. As a practical matter, these government can’t just void most contracts, including contracts the government is a party to, for the purposes of generating tax revenue.
All of which is why most real-world wealth taxes limit scope to a handful of liquid, legible securities and similar. But as a percentage of wealth, these are pretty small so you don’t collect much revenue.