We are approaching the issue from different angles. While you are focusing on theory, I am speaking from the practical aspect of the matter. No matter how independent the trust system is with the merit system, they compliment each other.
No matter how quality your post is, once I see negative tags and check the reasons for the tag. If they are legitimate, I'll not send a merit to you. I believe other members of the forum does same, no matter how good you are, immediately you have legitimate red tag from reputable members of the forum, your chances of receiving merits are slim.
The merit system and trust system are two completely different systems and they do not complement one another in any way i can think of, let me quote Theymos' post regarding sending of merits
While we will not be directly moderating this, I encourage people to give merit to posts that are objectively high-quality, not just posts that you agree with.
A member with a legitimate negative tag can make high quality posts and deserves to be merited, it should not put them in a different position from another member that has no negative tag. It is yours to decide how you give your merit, what i am just bringing to the fore is that negative feedbacks is not and should not be a criteria when sending merits, you would be better of looking at the quality, helpfulness, effort, post history and other things, but not negative feedbacks.
Since scam is not moderated, which means a notorious scammer would not be banned, that's my own means of paying back scammers. Well, it doesn't actually matter because I'm not a merit sourece.
Tag them, add them to your distrust list and warn other members about their bad reputation; but if you see a post of them that is worth meriting, you should merit it, but well like you said it doesn't matter, your merit is yours to use in a manner of your choosing.