Trust ratings aren't moderated. There are no hard rules, and you can't objectively say that someone is engaging in trust abuse. But if someone thinks that you are giving negative trust unreasonably, then they will remove you from their trust list.
What about if somebody thinks that positive trust is being given unreasonably, will they also remove you from their trust?
Say, for example, someone was giving their alts positive trust, would you personally consider that to be acceptable?
Also, while you are talking about trust, would it be fair to say that Default Depth 1 is effectively your personal trust list?