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.
But the reasoning is if you cheat merit then you're likely not a very trustable person as it's deceptive/questionable behaviour. Merit isn't really a system to replace activity but an add on to it because anyone can cheat activity just by logging on once a fortnight to make any old sort of spam post but this stops that.
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.
It will slow them down for sure and mass account farming just probably isn't worth the time or effort now unless people find ways to easily trade merit under the noses of the community, but not punishing those that are caught doing so is a slippery slope. If it becomes nonpunishable to trade or sell merit then the practice will become rife and defeat the entire purpose of the system in the first place and that's what I worry about not handing out punishments for people.