For me, when I'm trading, I try to show the pirate I'm not going to run anywhere by cutting my engines (sometimes even before they CD me) and talking to them.
From my pirate's point of view, I'll give any trader who comes near a train CD, then I'll start to RP. No point in saying anything if they're just going to cruise right past you. However, I like talking to traders, and I even have a set of /setmsgs which should relay that to a trader who'd rather run than talk (each one getting gradually madder until I decide that it's time to destroy the trader who's just spamming cruise)