@Occam Razor You mistunderstood all what I've written in my post. Trader can decide if they want to pay right away, try to impress pirate with negotiations or - what neither party wants - trader going boom. Credits can be earned very quickly, so paying up e.g. 2 million credits for cargo that gives you 17 million credits isn't a great loss. You also should remember that roleplay of unlawful ID is to pirate - to gain either credits OR cargo - so most of the guys aren't there to annoy you. They are doing the roleplay of the faction they represent.
And I say that both as a trader and as a pirate here.
P.S. If you see that pirate doesn't want to negotiate, just pay up without further questions. You should take into consideration that pirates seeing the trader prolongs the encounter may be caused by awaiting for e.g. local police/navy.
