if every trader went after every pirate that pirated them (sucessfuly). It would constatly be a string of player death notices. It's bad roleplay, and frankly, bad form. They got you, be done with it. all you can do now is file a 'police report' and/or put up a bounty (which would cost you more, but inconvienence them). And who's to say that this trader doesn't come back in a capitol ship? Its a pain in the butt. Most pirates will let you off for about 2-4 hours after you've "donated" to them. letting you continue your trade run in relative safety.
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I really wanted to make this sound eliquent... but I'm writing this at 2 in the morning where I live... so bear with me.