Happened at least once, when someone make bots that neg-repped everyone, so bots got banned and bad reputation removed
Yeah , negative trust gets removed only when it is spam.
If anybody with huge trust negs you today saying "Because he stole my cheezburger" , there is nothing you can do nor the admins/mods will do.
As long as you don't put dozens of repetitive negs , you can still give people negs for no good reason.
I don't think it's true that there is nothing you can do if someone (part of the default trust list) gives you unwarranted negative trust; if the other person can't be reasoned with and the abuse is obvious, you can at least contact whomever added that person to his/her trust list and ask him/her to remove them from the list. It won't remove the feedback, but it will remove the red trust warning that shows in posts and PMs.