VAT is not the only tax you pay. In Poland, depending on the kind of business you are running, apart from the value added tax, you are also paying tax on either profits or revenue (depends on what you do, if you do software - revenue tax is preferred because the rate is lower and you have effectively zero costs).

Of course it gets further complicated if your company is a standalone legal entity, but in that case you have a lot more funny scenarios, e.g. you can go to jail for acting against the interest of the company you are the sole owner of.

All countries have an "exception" for cash transactions. However, only within limits; the government investigators can indirectly infer and estimate unreported revenue.

I don't know exactly how many, but I know about 5 with VAT and exceptions.