There are two absolutely sure things in life:
Death and Taxes.
MJT: Actually, I agree with your premise.
In a lot of counties there is a goods tax and a services tax, at some rate or other. Every time a service is charged for, a tax on that service has to be paid.
If a good(s) has a value added to it, a tax on that extra value has to be paid.
If a coin is sold, that is a service. Tax man says: "tax please!" Legally, that should happen every time that coin is sold by a business.
When buying and selling takes place between private individuals (instead of a registered business), the Tax Man has no way of finding out if a transaction has taken place. In this case, no tax.