Just to emphasize what Ironhide is saying, leave an official reference! This forum is great to tell people of good traders, however you only get a small sampling of a trader's worth by scrolling down the page.
Your reference score is the currency that we as prospective traders use to determine how you may handle a deal. References from another site only show how you have handled a deal there, and even though that does have some merit, it's just not the same. Your Bartertown feedback helps the community as a whole. The more people use it, the better it is for everyone on the site.
So, like Ironhide said, take a minute, go to the tab, and leave a reference for your trading partner.
Lower rating? I ask that you ship first. Also, if I offer a stupidly good deal and you try to negotiate even lower...don't call it bad communication that you didn't get a reply. I deleted the message.