Received Negative Rep on Steamtrades Despite Never Contacting Nor Trading With the Reviewer

Hello,

Today I received my first negative rep on steamtrades by a person that I have never contacted nor traded with (I checked my replies section page, and his name never popped up) as well as my previous trades, which also turned up with nothing. And his comment was, "Sh**ty manners." However, from steamtrades' rules, you can't leave rep such as "rude, etc." and if you didn't trade with them. What's weird is that he had +5, -0 on his page. And also, I myself believe that I conduct myself in a respectful manner, my "rudest" gestures on the site probably telling potential traders that I would not like to trade Tomb Raider for the Humble Origin Bundle non-BTA because I can just get it for $1. What would be my best course of action to potentially remove this? Thanks!