It looks like no matter what if the last feedback you receive is negative then you will either have a ?? ? Trust score or a negative score. Look at TECSHARE for example, his rating from Vod means he has a question mark rating.
Also TF has a negative 9999 rating lol.
not always
I have seen users who received both positive and negative feedbacks and still has black trust ratings with first number 0
Edit: looks like trust system is not completely done, i have a seen a user who received 2 positive trusts around 6 months ago and few later as well as few negative feedback but still his trust rating is black with first number Zero (0). it should be either green or red because trust ratings are old. also total number of users who sent him trust are higher on his trust page then shown in third number in trust score