I wouldn't be opposed to a set upper limit for demands, something to say "Look, if you go beyond this point you're just being a prat."
It'd be good if we could find a balance between whats in character and whats good for gameplay, asking too much from a trader will simply put people off trading which means no fun for pirates, its happened before and it sure as hell will happen again unless attitudes on both sides improve. I mean for goodness sake if folks are only trading when its low population couldn't that be a sign that things aren't working out?
Calling people names or outright dismissing them is just childish and gets us nowhere.