[Admins]

And the taxes will be an important thing for the kingdoms. When the tax is too high for you then you can just drop the items, but it's risky and you cannot complain when the other one steals the stuff.
The same for market stands: they are not really needed since you can trade it directly, but they make thinks easier for you and you possibly get more money in less time than when speaking with all people and spending hours on negotiating good prizes. For that service you pay a little tax, which will depend on the kingdoms.

In real life you need to pay taxes when buying stuff from other people or trading valuable items.