I noticed this on a discussion board today:

One of my favorite little bits of history is the way the king of Denmark, when Denmark encompassed at least the southern parts of Sweden, assessed taxes on ships passing through the waterways between the North and Baltic Seas. Captains of ships passing through were allowed to declare the value of ship and cargo without any recourse by the taxing authorities. On the other hand, the taxing collectors were authorized to purchase said ship and cargo at the declared value if they thought it would be profitable.

I like it!