Evaluating a publicly traded company is pretty easy. Stock price times the amount of stock = value of company.
However evaluating other forms of companies is a lot harder. Using the same formula is possible (if there is stock) and otherwise you can still look at the equity value, but it will only say so much. Generally looking at future cashflows is a pretty good way of evaluating a company, but there are loads of things you can have discussions about regarding this method (called the discounted cashflow method). There are also others and I have been part of evaluating a company and it's a fair amount of work. So it's not something you can really do on a yearly basis for tax reasons.
There are other things you can do like looking at how much wage the major shareholder has or how much they have lent from their company. Both to themselves and to family/friends. In NL we kinda limit the amount you can loan from your own company.
Luckly for the whole situation most billionaires mainly have stock in publicly traded companies. Either directly or indirectly so that is taxable.
Yeah that is fair, but I preferred that a lot more than just using the 3mm jack on my Redmi Note 13 Pro. Man the DAC in that thing sucks.