If it is wise, you...
... get what you want
... (in a good case) you get good rp back
If it is not wise, you...
... get a running trader
... who never said a word to you
... and who depending on skill, ship class and armor, you will not even blue message
... will still likely get a blue message and the "good feeling" to have killed a "silent powertrader".
If someone says "drop all cargo", I fight and run. It's a terrorist demand in my eyes, IF the pirate cannot carry all the cargo.
Just make a demand that does not cause more harm than necessary and you will find that people respond well to real piracy play. Be an ass, and you will be treated like one. It's really that easy.