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.