If the problem is with the user spamming, the right approach would be to get a temp ban in place.
Negative trust just seems wrong.
I think a temp ban would be better indeed, but from what Im told its difficult to reach staff members that can issue one.
Then the admins should have a discussion about delegating this power to a few of the others as well.
Perhaps global moderators can be given the power to issue temp bans as well.
Admins: can do everything imaginable on the site. They however can't delete their accounts.
Global Moderators: can perma ban, nuke newbies, see and handle reports from all sections, and see reported PMs.
Moderators: can see and handle reports from their sections and nuke newbies
Patrollers: Are essentially Moderators but can only do moderator tasks for newbie members.