Yeah, I suggested that earlier as well: Try role-playing on this role-play server. Maybe you'll get used to it some day. Taking all the trader's cargo is perfectly in-RP in many situations (and not doing so can even be stupid in some). Of course not in all of them, most situations would be less harsh, if the pirate is just trying to milk you and not ruin you (in-RP). Yes, some pirates would in-RP try to ruin you. For example Hackers against Liberty Corps.
The original question: Killing a trader after he paid is a no-no.