The threat of death is the biggest tool for stopping traders.
Let pirates act like pirate for Disco's sake. It seems ooRP to make a demand from some one you know is about to get away only so you can blast them.
This is embrassing the mechanics more tightly than the realism.
With out this it is easier to pirate gunboats than trade ships. At least then they stand to lose system access for not complying.
I'll keep trying but I wont be pirateing as much thats for sure. I'll have to find new ways to engage new players. When pirateing is the biggest window to new encounters there is.