The post that was quoted here has been removed
I had those concerns, too, but it works on eBay, where the same issue seems to apply. One of the factors which seems to help there is that feedback is two way - if you give negative feedback, you often get tit-for-tat negative feedback, but then other users can read the feedback and judge who to believe. For example, suppose user XXX plays user YYY and they give each other negative feedback as follows: "YYY: Player XXX is a cheating ####", "XXX: I don't understand why YYY is saying that about me. I beat him fair and square. I have asked YYY to explain why he said that and he hasn't replied, so I have left him negative feedback in response to this unfair comment." If you then look and see that YYY says that about everyone who beats him, and XXX gets generally good feedback, then you can draw your own conclusions.