This is really funny. Feedback by nature should not have ACLs. This system promotes cheating since people can privately agree to add each other (or pay someone with a higher level) and gain powers. Also the system is way too convoluted and unfair towards Newbies and Coppers. Anyone with powers can stick a 'scammer' sticker on a newbie and the world would think so as well, they have no opportunity to clarify it, they would leave a review thinking that the world can read it, but they would be ignorant of the truth. The system should atleast make it clear that although they are leaving a counter review, it won't be visible to anyone except them.
It's fair since each users can include and exclude any users, now the question is how many users are going to trust you over him?
No this is not fair since a new user who has never interacted with either me or the person who left a negative review can only see their review, not mine! So no, this is unfair. Also, So to answer your question, ofcourse users are going to believe them since my part has been silenced systematically!
I will not disagree with your point "privately agree to add each other (or pay someone with a higher level) and gain powers" because definitely it's possible and no one can know behind them. But, the list of include and exclude users, feedback etc are completely transparent, if it's really suspicious or someone misused the power, other DTs can kick him from the DT network.
If you think you're correct and you didn't deserved to receive negative feedback, then create a thread in Reputation section and explain the case, it's the section to discuss about feedback.