To put a long story short, we have a land bridge between two political bodies. The bodies of whatever surrounding the land bridge is toxic and impassable. Other land bridges exist. The individuals manning the toll-castle are loosely aware of their existence. The merchants themselves are, of course, not a monolithic entity, but most generally accept that there are alternative routes to other political bodies (in simpler terms, other political entities exist).
There is a lot of thoroughfare, we've got traders, merchants, immigrants, raiders all showing up.
The transit toll at present is a 25% tax on cargo value. To keep merchants from understating the value of the cargo on which the tax was computed, the right to purchase the cargo at the stated value is reserved (or outright seized) Anyone importing 'sinful goods' (like alcohol, or cigarettes, or drugs, or pornography) has to pay a additional 25% on top of the baseline 25% (so 50% total).
For those who aren't traders or business people, ie, ordinary travellers/tourists/immigrants. All they have to do, is buy a 'official stamp' to mark out their travel pass, and then pay the head-tax.
So my question is quite simple, what is the most likely reason that people are willing to put up with such high rates)
