Well, it's OORP for a trader to say "Kill me it's cheaper" If you push the issue they can always find a way around if. They just have to come up with an RP way to do it. "I don't make deals with smelly pirates." and then try to run.
Of course if you really want to have some fun and they happen to be flying a transport or a train.....blow off all their cargo pods and turrets and let them go.