i gave you the example, baltar. - if you ask for a non specific amount, the victim can give you a "non specific" amount with which you MUST be happy with.
its a deal - a trader fulfils your request ( which is unspecificly "a donation" ) and for that the pirate lets the trader go. - if the pirate blows up a trader that fulfilled the pirates request, it would be a violation of the rules.
-- you cannot tax a trader for 3 million - AND kill him afterwards.
so you cannot ask for "a donation" receive "a donation" ( which could aswell be a nice word for all that matters or the trader wishing you "a lucky day and that he will pray for your fortune" - which certainly counts as a donation, too ) and then say "no no, i meant you must donate MORE or you die" - thats not the way things work.
[i know that example sucks - but who can tell what the other person considers "a donation" - praying for one can aswell be a donation as giving you 100million credits]
so, if you ask for a non specific amount of tax, you must live with "a non specific amount". - the joke is on the pirate then.