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In addition to what’s already been said so far, and having separated Trust from Flags (they’re two different sets of feedback, though often related), focusing on the Trust System, one interesting thing to know is that feedback and scores provided by inactive accounts will remain there forever (or so to say).
By this I mean that, since Trust feedback can only be removed by the person who gave the feedback (and often chances are slim of this actually happening), they are even worse if the giver’s account goes off the grid (0 chance) ...
Now people often just look at the Trust scores (numbers), and assume that the account is untrustworthy because of the numbers they see, though one should take that as an indicator, and dig into the feedback itself (both Trusted and Untrusted) to see the descriptive nature of that negative Trust.
Bear in mind that Trust counter values (positive; neutral; negative) display values based on your Trust list. The vast majority used the default Trust list, whilst a reduced set of people use a Customized Trust list (like I do). The values one sees on these counters may differ to those seen with a default Trust list (i.e. I could be seeing +0 / =0 / -2 whilst you could be seeing +0 / =0 / -1), and the feedback could visually move section from Trusted feedback to Untrusted feedback or vice-versa).
The counters show only values derived from your Trust list (be it default or custom), and correlate to what´s seen on the Trusted Feedback (meaning not under the Untrusted feedback section). Since, as said, most people have a default Trust List (level 2), Feedback from the DT network (up to level 2) are what count towards the Trust counters for the most. That’s why, in general terms, people are more concerned with trust received from DT1/DT2 than with trust received from other accounts. Note that DT members vary over time, which may change the impression of the received feedback one way or another.
And no, trusted feedback has historically not always been used in accordance to what it was intended for (commerce related). For example, my trust profile has a bunch of positive feedback which is not commerce related. It also includes 2 negative ratings under Untrusted feedback, both retaliation for having tagged them first.