lols, red mark is sometime not a serious matter, it doesn't mean that all red marks are scammer and likely criminal, sometime it serves as warning to people specially when they are reported repeatedly, or spotted out of the blue, you know, I saw your mark, in connection to merit issue.
Just apology to the marker not to repeat the same mistake again, they are particularly strict with the rules today and since there are a lot of bees making noise on the forum, some people are being pinpointed by their wrong doing.
Apology sincerely and if they don't forgive and remove it, just make curse, joke. Just apologize.
I'd really not be comfortable if there was such a system, and no, i really don't think that's what red trust is most used for. It literally states the following: "You were scammed or you strongly believe that this person is a scammer."
If this would be given simply on suspicion/as a warning i think it would be extremely skeptical to abuse.
You can't do anything sadly. If whoever left you the negative trust is not responding then you will have to live with it.
You might not be able to remove it, but if you feel like the trust rating you were given is false ( which does seem unlikely in this case), you could ask DT1/DT2 to counter your negative trust. ( which does seem unlikely in this case)