The issue of retaliatory feedback could also be addressed by having a comment section where a person could respond to their own feedback.
Allowing retaliatory feedback in any way results in those in the DT network can engage in shady behavior and scam for amounts less than the value of the value of the person they are trading withs reputation as upon the receipt of a scam report the person reporting will expect a negative rating themselves. This is especially true considering that many disputes are not black and white.