The Bundschuh prided themselves on not demanding anything, simply asking for donations. If the trader said no, depending on the goods he was carrying and the Bundschuh, he would be let go freely. (Goods like Diamonds etc on the run might end up getting you a nasty repair bill, usually not death though)
The non-specific demands actually worked very well. It gave us an indication of the sort of characters we were dealing with, and perhaps our respect or fear on the server. After all, a rich man offering 1 million is not the same as a poor man offering the same.
It is the offer that is of importance. To be brutally honest, we didn't just do it for the money since trading actually makes far more in the time period, but some find it far too boring.
However I do think that when you start to limit people to Demanding donations, then it removes a lot of roleplay.
Definition of donation:
1. The act of giving to a fund or cause.
2. A gift or grant.
This allows for forceful donations. Plain and simple they are often not-so subtlely hidden demands BUT they are not technically demands, and so any attack by a pirate due to it is illegal.
I personally do not like such wide spread abuse of the word 'Donation' but it is used often in threats. Do think that you shouldn't go strictly by the rules in this case since it would limit roleplay somewhat.