I am not sure if it can be truly assessed. There are many factors to value someone’s net worth. Is a persons intellect part of a person’s net worth?

Financial net worth of a person or corporation is the value of their assets minus their liabilities. From this definition, what’s put on the table can be fully assessed – which is what normally the case is – but what’s well hidden will remain unknown.

It’s very difficult to access ones wealth.since most income  and payment comes from outside banks consider women who sell  sex for money 

Yes, it can. But as you said, the self reported financial worth might not accurate in showing one’s true financial worth. However, if the authoritative body need to know one’s financial worth, they have every means to get it. And they can thoroughly identify every asset that belong to a particular person. 

Yes it can be assessed if it’s known but what is hidded can not be assessed.

Looking at the question again, yes financial net worth can be assessed. The thing that would be difficult to assess would be potential or future earning capacity

I don’t think this is 100% possible, because of changes in currency and stock markets. It’s possible that, a person can lose many billions in just a single day because of changes in currency and stock markets!

Again this position change from time to time, one can make an assessment today but within a single day, this position can go up or down!
So I’d say that, t’s not easy to make a realistic assessment.

Absolutely no. Very hard. Even a poor man net worth is difficult to be truly assessed. 

The old fashioned method of finding your net worth is was by subtracting all liabilities from assets. An asset being anything you own that has monetary value and liabilities are things such as loans and mortgages. Obviously this doesnt include intellect/ knowledge and future earning capacity but that also isnt realised because its not actual if you die tomorrow.