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 dont think the merit and trust system are all that closely related. I'm under the impression that the merit system is to replace the old activity system, and nothing more. Saying that ranking up an account is solely for account farmers and spammers isn't accurate. Plenty of people not involved in ad campaigns or account sales will want to rank up their accounts to lift their posting limits, to be able to post images, just for grins, etc. Of course, the new system is designed to prevent spam just for the sake of raising (activity) an account's rank.
asking for/buying trust/reputation = untrustworthy behavior
buying accounts = trying to buy reputation
begging for merit = trying to ask for reputation
These correspondences should be accepted by all members... but unfortunately, some do not view it this way (typically account traders).
Non malicious false positives are going to occur in pretty much every system. As long as the rate is very low, it is fine.
As for actmyname's quote above, I follow until the last statement. I agree with the bolded, but disagree with the underlined statement. As I just said a moment ago, I don't think there is a very strong link between reputation and merit. And I don't think the non malicious false positives are going to be low, let alone very low. Mixing the two systems is a pretty slippery slope. Begging for merit is obviously annoying, but there are a lot of unknowns with what is acceptable.
The value of 1 merit point is widely different to each person. If someone posted something and say I gave them 1/10/25/50 merit points, everyone might think that is extreme, but maybe its been a point I've been trying to get across for years, and seeing someone else say what I've been thinking gave me an overwhelming feeling of joy, hence the reward. Now, that guy is my friend/alt whatever allegedly, or I sold them merit. So I've now got a red mark for what is essentially my opinion.
The merit system should slow down spammers and account farmers, will it stop them completely? No, but if it helps cut down on them, the moderation staff should be able to handle the ones that slip through the cracks.