I think you are confused here. If you add someone to your trust list, that should be because you think that person leaves good feedbacks and has a good trust list. In theory, if that person gets red tagged, should not change your perception of the ability to leave feedback that he has in many cases. Now, there are times when someone is massively red tagged as a scammer and then people stop trusting him in general, so they also exclude him from the trust list.
Remember they are two different things, and I'm going to bring you a quote from LoyceV here from a thread you might be interested in reading:
Trust feedback: leave feedback to people you trust or don't trust. Or leave neutral comments.
Trust list: a list of people who's judgement on others you trust (username) or don't trust (~username).
Of course, you can delete the feedback or change a positive for a negative or neutral and vice versa.