I am new so i am not real sure on this. I think if i read correctly you can as a pirate ask any amount within reason (i guess that would be determined if a complaint was filed) so 10 mil from a merchant running an advanced train for 4 hrs is reasonable unless he just bought it and is broke (i am sure this line is used a lot) but say the pirate has a grudge against a merchant trader for getting away while he was busy with another merchant or just plain in a bad position to stop the trader so when he stops him he demands say 50 million credits knowing the merchant will not pay just so he can blow him away. I think if a complaint is filed in that case the pirate would be sanctioned.
This line however disturbs me.
"(and he didn't killed me, it was a dragon destroyer biggrin.gif)"
That sounds as if you were in a Dragon destroyer and if so and you were pirating you need to be sanctioned for pirating in a cap ship That IS against the rules.