Whenever a new feature, like merit or the feedback system is added, it takes the community a few weeks or months to figure out what is or isn't acceptable. I'm personally of the opinion that merit issues aren't related to feedback, and you shouldn't get negative feedback even for "abuse" of the merit system, whatever that ends up meaning.
Its kind of a rough position to be in, but you shouldn't worry about it too much.
Ironically the merit system was introduced to try prevent people from leaving negative feedback on poor posters. It's a tricky situation to police but
people shouldn't be allowed to trade merit or leave it for their alts as it's deceptive and defeats the purpose of the system in the first place. I can't really see any other way than negative really but users shouldn't be allowed to get away with it otherwise everyone will just do it. At least if there's the threat of negative for users caught engaging in it then most people will think twice about it. If there's nothing to lose by attempting to trade merit then the practice will become rife.
I think you are wrong about this, and I will explain why.
Ignoring the merit that everyone received at the introduction of the merit system, users will receive merit because someone believed they in some way made a good post, and decided this person should receive a portion of the limited number of merit points this person can send. The fact that there are a limited number of merit points, along with the fact that merit points ultimately allow someone to earn money via signature campaigns means that merit points give value to the person receiving said merit. I don't think it is appropriate to tell people they have to use their valuable property in only certain ways, especially when these "rules" will frequently change (often after the fact), and will not be applied evenly.
If someone were to buy merit to participate in a signature campaign (or otherwise), and are a crappy poster, they will either get banned, will not be hired to participate in a signature campaign, or both. The buying of merit would serve as somewhat of a non-refundable deposit allowing them to participate in a signature campaign.
At the end of the day, a person will not be able to receive merit if at one point, a merit source (who cannot --in theory-- sell merit) decides it will be appropriate to issue merit to someone.
In reality, when you are sending 1 merit to someone, you are effectively sending them ~1.9934 merit including the merit they can send to others.